Chapter II: Part 2

Before sugar can be used by the human system, it is changed into grape sugar, or dextrose, (another form of sugar) by a ferment in the small intestine called lactose. Milk sugar needs less chemical change than other sugars and is taken almost at once into the circulation.

When an excess of sugar is consumed, it is stored within the body as glycogen, until required.

Sugar is perhaps a better food than starch, because less force is required for its digestion and it is easily assimilated, being more readily converted into dextrose than are starches. Moreover it furnishes the needed heat and energy to organisms that have no power to digest starch. Milk sugar is a part of the natural food for the infant, because the infant has not developed the ferment necessary for starch digestion.

Sugar may be oxidized within a few minutes after eating, and, for this reason, it is eaten by those who require to use an undue amount of muscular strength. It yields heat and energy within thirty minutes after eating and, in times of great exertion or exhausting labor, the rapidity with which it is assimilated gives it advantage over starch. Used in limited quantities, therefore, according to the muscular or brain power exercised, sugar is one of the best foods for the production of energy. Where much sugar is eaten less starch is required.

It is also said to prevent fatigue, a man being able to do seventy-five per cent more muscular work with less fatigue after consuming about seventeen and one-half ounces of sugar dissolved in pure water.

It might be inferred from the above, that starches could be discarded and replaced by sugars, but a small quantity of sugar soon surfeits the appetite and if the foods were confined to those with a surplus of sugars, sufficient food would not be eaten for the needs of the body. This lack of appetite, occasioned by an excess of sugars, is due, partly, to the fact that the gastric juice is not secreted as freely when there is much sugar in the stomach.

Because of the slower secretion of gastric juice and the surfeit of the appetite, sweetened foods are not used at the beginning of a meal, and, while a moderate amount of sugar is desirable, a surfeit is to be deplored.

While sugar is not converted into fat, it is so readily oxidized and thus supplies heat and energy so promptly that the starches and fats are not called upon until the latent energy in the sugar is used. Those who wish to reduce in flesh should eat it sparingly that the starches and fats may be called upon to furnish energy, but sugar should be as freely used as the system can handle it, by those who wish to build up in flesh.

Broadly speaking, about one-fourth of a pound of sugar, daily, in connection with other foods, is well utilized by the system, the quantity depending upon whether one leads an active or a sedentary life.

Candy is often made from glucose instead of molasses or cane sugar, and while glucose is wholesome, it undergoes fermentation readily. Much candy, unless one is actively exercising, tends to indigestion.

The desire of the child for sweets is a natural one, because it uses so much energy, and sugar supplies this energy with less effort of the digestive system. When the child begins to eat more solid foods, if sugar is used in abundance for sweetening, it is no longer attracted by the mild sweetness of fresh milk, and it is well to cut down the allowance of sugar, when the child turns against milk, in the hope of restoring the taste for this valuable food. Many of the best authorities state that the child, up to its third year, should never be allowed to taste sweets, in order that the appetite may not be perverted from the natural sweets of milk.

Sugar is better supplied the child in a lump or in home-made candy, rather than in the sweetening of porridge, oatmeal, or bread and milk, etc.

Sweet fruits, fully ripened, contain much sugar and should be freely given to the child. The natural flavor of fruits and grains is very largely destroyed by sugar, which is used too freely on many articles of diet.

Most vegetables and fruits contain sugar,—indeed sugar is the only nutriment in many fruits. The sweet taste in all fruits and vegetables is due to its presence. Sweet potatoes, beets, carrots, parsnips, turnips, grapes, figs, and dates are especially rich in sugar and when these are furnished with a meal, in any appreciable quantity, the starches should be restricted—notably bread, potatoes and rice.

Harvesters, road-makers and others, who do hard work in the open air, can consume large quantities of sugar in pie, pastry, etc., which are difficult to digest, while one who lives an indoor life, should refrain from an undue indulgence in these.

For one who is undernourished, sugar is a desirable food, if the starch be diminished in proportion as the amount of sugar is increased; but the inclination in sweetening foods is to take more starch than the system requires, since it is the carbohydrate foods which are ordinarily sweetened,—not the proteins.

On account of the latent heat and energy, sugars are more desirable in cold weather than in warm. Nature supplies them more abundantly in root vegetables for this season. More puddings and heavier desserts are eaten in winter.

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[Sidenote: Starch]

Starch is one of the most important carbohydrates used for nutrition. It is formed by the chemical action produced by the sun’s rays upon the cells of living plants, from the carbon-dioxid and water in the air and in the soil.

Corn starch, sago, tapioca, and arrowroot are practically pure starch. Cornstarch is from young maturing corn; tapioca is from the meal of a tropical plant, cassava; sago is from the pith of the sago palm; arrowroot is from a plant of the same name, a native of the West Indies. Rice is almost pure starch, while wheat and other cereals contain from sixty to seventy per cent.

Starch lacks flavor and for this reason all starchy foods are seasoned.

All starches must undergo much chemical change by action of the saliva, the intestinal juice and by the liver, before they can be used by the body. They are first converted into dextrine and then into maltose (animal sugar). The digestion is begun by the saliva in the mouth and continued in the stomach by the saliva swallowed with the food. If the saliva fails to digest all of the starch, either in the mouth or the stomach, it passes unchanged into the intestines, where it is converted by the amylase of the intestinal juice, first into dextrine and then into maltose, or sugar. It is absorbed into the blood as sugar. After the digested starch (maltose) passes into the blood it is spoken of as sugar. Before it is converted into energy it is again changed in the liver into animal starch (glycogen) and stored for a time in the liver. When the system is ready for it, it is again broken down into sugar, because in the form of glycogen it cannot be absorbed into the blood.

The chemical process used in the formation of glucose, from the starch in corn, is allied to the change in the liver, from starch into sugar.

The starches and sugars are really the “reserves” or “go-betweens” of the body, being stored until needed.

If starches are consumed in unduly large quantities, without sufficient exercise to burn them up, they overload the liver and clog the system.

Starchy foods should not be given to children before the starch converting ferments are formed, nor to one in disease where these ferments are interrupted.

Nitrogenous Foodstuffs or Proteins

The proteins form heat and energy when the supply of sugars, starches, and fat are exhausted, but proteins, alone form muscle, bone and sinew. They are, in this sense, the most important of foods,—they are, also, the most costly.

The foods most rich in proteins are meat and eggs. These have undergone chemical changes from the vegetable kingdom being built up into more complex compounds in the animal kingdom.

Meat and eggs are the tissue builders. In this connection it may be well to state that blood is tissue; thus meat and eggs build the blood, as well as muscle and sinew.

Nitrogenous foods, or proteins, are so called because of the large proportion of nitrogen which they contain. All nitrogenous foods contain considerable carbon—mostly in the form of fat in the meat elements—but the carbonaceous foods contain so little of the proteins that they do not appreciably enter into the nutrition,—the carbon and nitrogen in the carbo-nitrogenous foods are more equally divided.

The nitrogenous or protein elements in the body constitute about one-fifth of its weight. They make the framework, forming the basis of blood, lymph, muscle, sinew, bone, skin, cartilage, and other tissues.

Worn out body tissues is constantly being torn down and eliminated and the protein in the foods must daily furnish material for repair, as well as for building new tissue in the growing child.

A young animal’s first need is for growth, not having learned to exercise sufficiently to use much energy, and the first food given is an animal product—milk to babes and other mammals, while the young of other animals are first fed upon eggs.

The nitrogenous foods are required in smaller bulk than vegetables and fruits; they are more concentrated and contain less waste. According to recent experiments, the average adult requires from two to four ounces a day of nitrogenous foods, to repair the waste, according to the proportion of nitrogen contained. Happily, where more is consumed, the system has the power, up to a certain limit (depending upon the physical condition and the daily activity), to eliminate an excess. It is needless to say that if the daily waste is not re-supplied, the digestion and bodily nutrition suffer. The system _must_ have the two to four ounces to supply the nitrogen daily excreted, or the tissues themselves will be consumed.

The proteins, of which meat is the principal one, are classified as

Albuminoids:—albumin (white of eggs), casein (curd of milk), myosin (the basis of lean meat and gluten of wheat),

Gelatinoids, (connective tissue of meat),

Extractives (appetizing and flavoring elements).

DIGESTION

Any discussion in regard to the digestibility of foods must be general, because food which agrees with one may disagree with another, and a food which disagrees with one at a particular time may entirely agree with him at some other time; therefore, before one passes upon the adaptability of a food to the individual, it should be known that this food agrees or disagrees with him under varying conditions.

The digestibility of food depends largely upon the physical condition of the individual, because the amount of digestive juices poured into the alimentary canal is influenced by this condition, particularly by the condition of the nerves. If sufficient juices, in proper proportions, are not poured into the digestive tract, the foodstuffs are not made soluble for absorption into the blood. Digestion is practically synonymous with solution,—all solid foods must be reduced to a liquid state, through digestive juices and water, before they can pass through the walls of the stomach and intestines.

Each individual should _learn to like_ the foods containing the nutrient elements which experience and blood tests have shown to be lacking in his case. The question of likes and of dislikes in regard to foods, is largely habit, and one can learn to like almost any food one wishes.

Where one forms the habit of discriminating too much in the food, or discarding this food or that, because at some time it has disagreed, due to the particular condition at the time, the mind approaches the table as a more or less pessimistic censor and the saliva and the gastric juices are retarded in their flow.

When one is exercising freely, so that the muscular and mucous coats of the digestive system are strong, the body will handle foods which, during sedentary habits, it would not digest. There are kinds of foods, however, which, to certain individuals, according to the chemical composition of the body, act as actual poisons, e. g., strawberries, cheese, or coffee.

It may be well to here trace, briefly, the progress of the food through the digestive tract and the action of the juices and the ferments upon it.[3]

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[Sidenote: Salivary Digestion]

The food in the mouth is mixed with saliva, which dissolves the starches, converting them into sugar. The starches are the only foods whose chemical digestion is begun in the mouth. They are first broken up into dextrin and then into the more simple sugar, known as animal starch, or _maltose_. Hereafter, in speaking of sugar, after it has been absorbed into the blood, the reader will bear in mind that the term refers not only to digested sugar, consumed as such, but also to digested starches (maltose), as shown on page 63.

It is important that sufficient saliva be mixed with the food, through mastication, that it may enter the stomach and there continue the chemical process of digestion of starch. If starches are not thoroughly masticated, sufficient saliva will not enter the stomach to convert the starch into sugar; the food will pass into the small intestine, which must then do more than its normal work of digestion.

The saliva consists of about ninety-nine and one-half per cent water and one-half per cent solids. The solids consist of ptyalin, sodium chlorid, sodium carbonate (baking soda), mucus, and epithelium. Ptyalin, the most important of these, is an active digestive agent; the mucus lubricates the masticated food; the sodium carbonate insures the alkalinity of the food; the salt is present in all secretions; and the water dissolves the food that the juices may more readily reach and act upon each particle.

The saliva flows into the mouth, more or less, at all times, but more copiously during mastication. Its evident purpose, when food is not present, is to keep the lining of the mouth moist.

The flow of saliva is controlled, to a great degree, by nerves which have their centers in the medulla oblongata. The sight of food, pleasingly served, or even the thought of food which one likes, will increase the salivary flow. This is one instance of the control of thought materially affecting digestion, and the importance of _forming the habit of cultivating a taste for all kinds of food_, is apparent. The stronger the relish for the food, and the more thoroughly it is masticated, and mixed with the saliva, the more perfect will be the first step in digestion. This first step of thorough mastication is all important, not only because the chemical action upon the starch molecules is facilitated by the thorough softening and mixing with the saliva, but thorough mastication also tends to prevent overeating.

Water encourages the flow of saliva and for this reason should be drunk copiously before meals, particularly where digestion is weak. It may also be taken at rest periods during the meal. (See page 44).

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[Sidenote: Stomach Digestion]

As the food enters the stomach, the gastric juice pours out from the mucous lining, very much as the saliva pours into the mouth. It consists of ninety-nine and one-half per cent water and one-half per cent solids, as does the saliva. The solids of the gastric juice are composed of pepsin, rennin, hydrochloric acid, and mucus. The mucus serves to lubricate the food as in the saliva. It also prevents the digestion of the mucous lining of the stomach itself.

The hydrochloric acid and the pepsin cause the principal chemical changes in the food while in the stomach, acting alone upon the proteins. The only digestion of starches in the stomach is that continued by the saliva. The salivary digestion proceeds until the gastric juice is secreted in sufficient quantity to cause a marked acidity of the stomach contents, when the starches are passed into the intestines.

Gastric juice begins to flow into the stomach soon after eating, but it is not secreted in sufficient quantity to supersede salivary digestion for from twenty to forty-five minutes.

The result of gastric digestion of proteins is their conversion, first, into albumin, then into proteosis and, lastly, into peptone, which is protein in a more simple, soluble, and diffusible form. In the form of peptone, the proteins are in condition to be absorbed.

If the food has been properly cooked and masticated the gastric digestion will be completed in one and one-half to three hours. If not properly cooked and masticated, the stomach digestion may continue one to two hours longer. It should, however, be completed in three hours.

The most readily digested animal foods remain less time in the stomach. Meat, as a rule, is easily digested, because the action of the digestive juices of the animal has converted the starches and sugars. The white meat of chicken, being soft, is digested in a shorter time than the red or the dark meat.

Fluids leave the stomach more rapidly than solids. Seven ounces of water leave the stomach in one and one-half hours, seven ounces of boiled milk in about two hours.

The flow of gastric juice, as the flow of saliva, is governed by the nerves;—the sight, taste, and smell of food, and the attitude of mind toward it, to a certain extent, regulates its flow.

After the food has extensively accumulated, during the progress of a meal, the stomach begins a series of wave-like movements called peristaltic waves.[4] These waves work downward through the length of the stomach towards its lower opening, known as the pyloric orifice. As the food is moved down the stomach by these motions, it is thoroughly mixed with the gastric juice.

During the early stages of digestion, the sphincter muscles of the pylorus keep the lower end of the stomach closed, but, as digestion progresses, the pylorus gradually relaxes to let the digested, soluble portion of the food pass into the intestine. If the food still remains in a solid form, by reason of being improperly cooked or poorly masticated, as it touches the pylorus, these sphincter muscles, almost as if they were endowed with reasoning faculties, close, forcing the undigested mass back to be further acted upon by the gastric juice,—the solid mass is not allowed to pass until dissolved.

If the individual continues to abuse the stomach and to cause it to work overtime, it becomes exhausted and demands rest; it refuses to discharge the gastric juice in proper proportion; the peristaltic movements are weak; and food is not promptly or forcefully moved along the stomach and mixed with the gastric juice. This demand for a rest is termed _Indigestion_.

To sum up,—digested sugar is dextrose; digested starch is first dextrin, then maltose (animal, sugar); digested protein is peptone; and, digested fat is saponified fat.

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[Sidenote: Intestinal Digestion]

The food passes from the stomach, through the pylorus into the small intestine. The first twelve inches of the small intestine is known as the duodenum. In the duodenum it is acted upon by the pancreatic juice from the pancreas, the bile from the liver, and the intestinal juices. These juices act upon proteins, fats, and carbohydrates. The bile acts upon the fats, while the pancreatic and intestinal juices act chiefly upon the carbohydrates.

As the food enters the intestine, it is changed, by the sodium carbonate, from the acid condition produced in the stomach, to alkaline reaction.

The bile exercises an important influence upon digestion, any disturbance in the flow of this greenish-brown secretion being very quickly shown both in stomach and intestinal digestion. It emulsonizes and saponifies the fats, it aids in their absorption, and it lubricates the intestinal mass, facilitating its passage through the entire length of the intestines. Thus, it is a very potent agent in regulating the bowel movements. A diminution in the flow of bile quickly expresses itself in constipation.

Fats are almost entirely digested in the small intestine. The presence of fat stimulates the flow of pancreatic juice, which, in turn, stimulates the flow of bile from the liver. For this reason, if the liver is sluggish, fatty foods are desirable. Olive oil is prescribed for gall stones to stimulate the action of the bile ducts.

Before the fat molecules can be absorbed, they must first be broken up into glycerin and fatty acids and further changed to a fine emulsion, which gives the contents of the small intestine a milky appearance. After they are broken up into these fatty acids and thus brought to the finest state of emulsion, they are readily saponified, being then soluble in water and in a state to be absorbed by the walls of the intestines. The fats are absorbed almost entirely in the small intestine,—mostly in the duodenum.

As a rule, the starches, or dextrin, will not be fully digested by the saliva and those which have failed of salivary digestion are acted upon by amylase (one of the solids of the intestinal juice) and changed to maltose, while the trypsin from the pancreas, together with the intestinal juice, acts upon any protein which has failed to be fully digested in the stomach, changing it into peptone. In the form or peptone it is absorbed through the “sucking” villi of the intestinal walls.

The food is forced along the intestinal tract by peristaltic or muscular relaxation and contraction waves, as in the stomach. As it is so forced, the nutrient elements, after being put into condition for absorption, are taken up through the villi of the intestinal walls by the portal veins and the lacteals of the sub-mucous lining. (See page 78).

It is now believed that a larger proportion of food is digested and absorbed than was heretofore realized, and that the excretions from the intestines are, in many cases, made up almost entirely of refuse, and of the catabolic waste of the system. In an ordinary, mixed diet, it is stated that about ninety-two per cent of the proteins, ninety-five per cent of the fats, and ninety-seven per cent of the carbohydrates are retained by the body.

_In digestion, it is of the utmost importance that the muscular, mucous, and the sub-mucous coats, and the secreting glands of the stomach and intestines be kept thoroughly strong and active, that the digestive juices may be freely poured out, the nutriment be freely absorbed, and the food be moved along the digestive tract. The strength of any organ is gained through the nutriment in the blood; therefore, daily exercise, which calls the blood freely to these organs, is imperative._

[Sidenote: Absorption of Food]

The greater part of the food is absorbed through the intestines, yet some proteins, which have been fully digested by the gastric juice, and certain fats, particularly the fats in milk, which are in a natural state of emulsion, may be absorbed through the walls of the stomach. However, the absorption through the stomach is small compared to that through the intestines.

The small intestine is particularly fitted for absorption. Every inch or so along its course the mucous lining is thrown up into folds, as if to catch the food as it passes toward the large intestine, and to hold it there until the villi have the opportunity to absorb it. These transverse folds of the intestinal walls are called valvulæ conniventes. The villi are fingerlike projections of the mucous lining of the intestines, which stand out upon the lining somewhat as the nap on plush. They have been called “sucking” villi, because during the movements of the intestines they seem to suck in the liquid food. As soon as the foodstuffs,—proteins, carbohydrates, and fats, are put in a dissoluble state ready for absorption, they are very promptly absorbed by the villi. If, for any reason, they remain unabsorbed, they are liable to ferment by the action of the trypsin, or to be attacked by the bacteria always present in the intestines.

The peptones, sugars, and saponified fats are rapidly absorbed, while the undigested portion, together with the unabsorbed water, the bile, mucus and bacterial products, are passed through the ileo-cecal valve into the large intestine.

That the large intestine is also adapted to the absorption of fats is shown by clinical experiments with patients who cannot retain food in the stomach, the food in such cases being given through rectal injections.

In the large intestine, the mass passes up the ascending colon, across the transverse colon, and down the descending colon, losing, by absorption, foodstuffs not absorbed in the stomach and small intestine.

While water and salt are absorbed both in the stomach and in the small intestine, the evident purpose in leaving the larger part of the water to be absorbed in the large intestine is that it may assist the intestinal contents in passing along. The water also stimulates the peristaltic movement.

As the food is absorbed through the walls of the alimentary canal, it is picked up by the rootlets of the mesenteric veins[5] and by the lymph channels,—the latter, through the abdominal cavity, are called lacteals. Nearly all of the fats are absorbed through the lacteals. The whitish color given to the contents of the lacteals, by the saponified fats, gives rise to the term lacteal, meaning “whitish.”

Nearly all of the proteins and sugars pass through the mesenteric veins and the portal veins into the liver. Here the sugars are at once attacked by the liver cells and built up into glycogen as described on page 81 and the proteins are passed through the liver into the arterial blood stream. A small portion of the proteins, however, do not go to the liver, but are passed directly into the lymphatics and thus into the blood stream, where they are again carried to the liver.

To sum up,—the larger part of the absorption of sugars, starches, proteins, and fats is through the small intestine, though some are absorbed in the stomach and a very little through the large intestine; while some water and salts are absorbed in the stomach and small intestine, these are largely absorbed in the large intestine.

FOOTNOTES:

[3] A knowledge of the mucous lining of the stomach and intestines, and of the tributary glands, such as the liver and pancreas, is important to a thorough understanding of digestion, and the reader is referred to “The Vital Organs: Their Use and Abuse” of this series. This takes up the study of the secretion of digestive juices, the conditions favoring normal secretions, etc.

[4] See “The Vital Organs; Their Use and Abuse” by Susanna Cocroft.

[5] For illustration see the frontispiece of “The Circulation, Lungs, Heart,” of this series.

The Work of Various Organs Affecting Digestion

The purpose of this chapter is to show the work of other organs than the digestive organs in converting the digested food to use in the body, in tearing down waste, and in eliminating waste and an excess of material above the body needs.

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[Sidenote: Work of the Liver]

The liver is commonly called the chemical work-shop of the body. The proteins and sugars are carried through the blood (portal veins) to the liver directly they are absorbed from the alimentary canal. As the food materials filter through the blood capillaries, between the liver cells, several substances are absorbed, particularly sugar, which is here changed into animal starch called _glycogen_. It is held in the liver for a few hours in the form of glycogen and then redigested by the action of an amylolitic ferment and again gradually given out into the blood in the form of sugar; hence sugar is subject first to the anabolic change of being built up into glycogen, and then to the catabolic change of oxidation and breaking down.

While the conversion of the sugar is one chief office of the liver, it also acts upon the proteins,—not as they are first passed through the liver in the blood, but as they are returned to the liver from the muscle tissue, partly oxidized and broken up into simpler products. The liver cells absorb and further oxidize and combine them into nitrogenous waste, which the kidneys throw off in urea.

The liver and the spleen also break up the pigment or coloring matter of the red blood corpuscles. As they become worn out, they are retired in the liver and the spleen from the circulation. The iron is retained by the liver cells and the remainder is thrown off from the liver, in the bile.

The liver is often called the watch dog of the body, because it is on guard for all poisons which pass through it in the blood. The large part of these toxic substances are absorbed through the alimentary canal with other foodstuffs. Many of them are the result of the fermentation of foods which are not digested as promptly as they should be, on account of an insufficient secretion of digestive juices, or a failure to secrete them in normal proportions, or due to inactivity of the stomach and intestines.

It surely is a wise provision of nature to supply a guard to oxidize, or break down these poisons and make them harmless, so that they do not pass to all parts of the body as poisons, thus affecting the nerves and the blood stream, and, through these, the entire system.

The necessity of correct habits of deep breathing will be readily seen, because oxygen is required to break down the poisons as well as to oxidize the waste of the system.

One example of the action of the liver in rendering substances harmless, is its oxidation of alcohol. From one to three ounces of alcohol a day are oxidized and made harmless in the liver, varying according to the individual and to the condition, at different times, in the same person. If the limit of one to three ounces is exceeded, the excess is not oxidized and intoxication results. These evidences of intoxication are in the nature of narcosis; _alcohol is now regarded as a narcotic along with ether and chloroform_.

It was formerly held by physiologists that alcohol was a food, because its oxidation liberates body heat and it was assumed that this liberation of heat, was the same as that freed by the combustion of fats, starches, and sugar uniting with oxygen. More recent knowledge, however, has unquestionably determined that heat, resulting from oxidation of alcohol, does not keep up body temperature; the pores of the skin are opened and there is a greater loss of heat through the skin. This really makes the system less able to resist cold. Large doses of alcohol actually cause a fall in body temperature and every force of the body is decreased in efficiency, while if alcohol were an actual food the efficiency would be increased. We are forced to the conclusion, therefore, that alcohol is a _pseudo-food_ as it is a _pseudo-stimulant_.

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[Sidenote: Work of the Muscles]

The muscles play an important part in the use of foods. Most of the heat is generated in them, by the sugar and fats coming in contact with the oxygen in the blood. This heat is liberated during every moment of the twenty-four hours, asleep or awake. Of course, more is liberated during exercise, since the movement of the muscles sets all tissues into activity and the blood circulates more strongly, bringing a greater supply of oxygen to them. It is always well during active exercise to stop frequently and fully inflate the lungs. The effort should always be made to breathe fully and deeply—otherwise the pressure of the liberated carbon dioxid will cause a pressure throughout the blood stream, particularly about the heart and in the head. This pressure is relieved when the excess of carbonic acid gas liberated has been thrown off by the lungs. Nature makes the effort to throw off the excess of carbonic acid gas by forcing one to breathe more rapidly while running or taking unusual exercise.

The oxidation changes are simply a combustion of sugars and fats, liberating latent heat as they are brought into contact with the oxygen. Exercise and a regulation of the amount of carbohydrates and fats consumed in the foods is the natural, scientific method for the reduction of an excess of fat.

A certain amount of protein is constantly oxidized in the muscles, also, being broken down into carbon dioxid, water and a number of nitrogenous mid-products. The carbonic acid gas and water are thrown off by the lungs and the partially oxidized, nitrogenous waste is carried to the liver, where it is further oxidized and prepared for excretion, through the kidneys, lungs, skin and intestines.

When sugar is carried to the muscles in larger quantities than can be utilized by them, it is often built up into animal starch and stored in the form of glycogen, similar to its chemical change and storage in the liver.

This storage of glycogen in the muscles and in the liver is a wise provision of Nature. It is a reserve to be called upon whenever the expenditure of heat and energy exceeds the amount supplied in any day’s rations.

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[Sidenote: Work of the Nerves]

The nerves oxidize food materials, but not to any great extent, excepting during nervous activity. During periods of rest, food materials are stored in the nerve cells in grandular form. They represent concentrated nerve foods and are the result of anabolic processes. During nervous activity they are oxidized and carried away through the blood and the lymph. This oxidation of the food, stored in the nerves, creates nervous energy and heat.

The energy liberated by the nerves resembles electrical energy.

Where one subjects himself continuously to an excess of nervous activity, all reserve food material, stored in the nerve cells, is used and the result is a trying nerve tension. Such individuals need plenty of easily digested food.

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[Sidenote: Work of the Lungs]

The lungs absorb oxygen and eliminate carbon dioxid. They occasionally throw off a very little organic material.

The carbon dioxid is carried to the lungs from the tissues through the venous stream and diffused through the capillary walls of the lungs. The oxygen is absorbed into the capillaries through the thin air sacs in the walls of the lungs.

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[Sidenote: Work of the Kidneys]

The kidneys do not absorb as do the lungs, neither do they perform any anabolic work as does the liver, nor catabolic work as the muscles, nerves and the liver. They simply throw off waste matter.

The blood passes through them in a transverse branch from the abdominal aorta. In its circuit urea, uric acid, urates, sulphuric acid, sulphates and sodium phosphates pass from the blood with the water and are thrown from the system; hence the kidneys are purifying organs, as are the lungs. The blood returning from the kidneys through the veins is pure, just as the blood in the pulmonary vein is pure, while that in the arteries to the kidneys and the lungs is impure.

The above substances cannot be thrown off from the lungs. They are the products of oxidation of proteins, partly of the living tissues and partly those broken down direct as they are supplied in the foods, in excess of the needs of the system.

Interference in the action of the kidneys results in a hoarding of these substances in the blood, and may produce an intoxicated condition known as uremic poisoning.

Water in abundance and diuretic fruits and vegetables, which increase the activity of the kidneys, should be taken where uremia is indicated. (Foods which cause a free flow of urine are called diuretic foods.)

[Sidenote: Work of the Skin]

The sweat glands also throw off an excess of water and salts. The kidneys and the skin are interdependent; if the kidneys are inactive the skin throws off a larger quantity and if the skin is inactive, or if for any reason the pores of the skin are closed, the kidneys are more active. This is evidenced by the sudden immersion of the body in cold water; the pores of the skin being closed the kidneys immediately act.

During the summer, or at any time when the skin throws off more water than usual, the kidneys are less active and the urine, being more concentrated, is darker.

The skin also throws off carbon dioxid and, to a slight extent, it absorbs oxygen.

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[Sidenote: Work of the Intestines]

The intestines, in their work of elimination, pass off all undigested matter. They also carry off bile pigment, bile salts, mucus, amino acids, and other decomposition of proteins,—also a little unabsorbed fats and bacterial decomposition taking place in the intestines. Coarse articles of food containing fibres which do not digest, such as the bran of grains and the coarser fruits and vegetables (though much of their substances are not food in the strictest sense) are valuable to increase the peristaltic movements of the intestines and to act as a carrying body to move the waste excretions along their course.

The combustion, or burning of fuel in any form, (oxidation for the release of latent heat and energy) always leaves some parts which are not used as heat or energy, and it is the work of the intestines to eliminate much of this refuse. When coal is burned, gas, smoke and cinders or clinkers, constitute the waste and if these were not allowed to escape from a stove the fire would soon go out—the smoke and gas would smother it and the clinkers would prevent the circulation of oxygen and soon clog and fill the stove. The same is true in the body—the carbonic acid gas not being allowed to pass off would soon put out the fires of life; it would poison the body and stunt the action of the nerves. If the nitrogenous waste (like ashes and cinders) is not eliminated by the kidneys, one will die in convulsions in one or two days.

The absolute necessity of a free elimination of waste will be readily seen.—If the engine is to do its best work, the engineer sees that it is kept perfectly clean—otherwise it becomes clogged, does inefficient work and the clogging soon wears out some parts. The same is true in the body,—clogging in any part overworks and wears out other parts dependent upon the work of the one.

Summary

Let us sum up the processes which the food undergoes in its conversion into condition to be absorbed by the body; in its absorption through the walls of the intestines and stomach; and the metabolic processes which it undergoes in being converted into heat and energy and again broken down and eliminated as waste.

_The Saliva_ begins the digestion of starches and sugars in the mouth. This digestion is continued by the saliva in the stomach.

_The Stomach_, when in normal condition, thoroughly digests the proteins. If any proteins fail of digestion in the stomach the process is completed in the intestines.

The _Intestines_, aside from their work of digestion and absorption, excrete bile pigment, bile salts, animal acids, mucus and other decomposition of proteins, with bacterial fermentation and putrefactions; also such food materials as are not digested.

The small intestine digests and absorbs the fats and continues the digestion of starches, sugars and fats when this digestion is not completed in the stomach.

The large part of the food is absorbed through the small intestine, though a small part is absorbed through the walls of the stomach and through the large intestine.

Fats are almost entirely absorbed in the small intestine. They are absorbed through the lacteals and are carried into the blood stream.

_The Liver._ The proteins and the starches (converted into maltose) and sugars pass into the liver. The sugar (including the sugar in vegetables, milk, fruits and that used for sweetening, as well as the carbohydrates which have been changed into maltose), is converted into glycogen in the liver, stored here for a time and again broken down into sugar that it may be in condition to be absorbed into the blood.

The proteins pass through the liver but are not acted upon by this organ until they again return to the liver through the blood stream, after they have been partly oxidized in the tissues. The liver further oxidizes them putting them into condition to be excreted by the kidneys and intestines.

The liver also breaks up the worn out red corpuscles, putting them into condition to be eliminated in the bile.

It oxidizes and renders harmless poisonous substances absorbed in the food, such as fermented food products and alcohol.

The _Muscles_ oxidize the fats and sugars liberating the latent heat and energy.

They partly oxidize proteins which are further broken up in the liver.

The _Nerves_ oxidize food materials stored in the nerve cells, providing nervous energy.

The _Lungs_ absorb oxygen and throw off carbon dioxid, watery vapor and some organic substances.

The _Kidneys_ and The _Skin_ purify the blood by excreting water, carbon dioxid and nitrogenous waste.

FACTORS INFLUENCING DIGESTION

As before stated, it is not the food eaten, but that which the body digests and assimilates, or appropriates to its needs, which counts; many factors influence such nourishment. The principal ones are the forceful circulation, the breathing of plenty of oxygen, and the resultant free elimination of waste.

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[Sidenote: The Appetite]

If one has no appetite, by far the safest method is to abstain from food until the system calls for it, or to eat but a very little of the lightest food at regular meal times; be careful not to mince between meals nor to eat candy nor pickles. Be sure that the lack of appetite is not due to mental preoccupation which does not let the brain relax long enough for the physical needs to assert themselves. One should relax the brain in pleasant thoughts during a meal.

If the appetite is lacking, because of physical exhaustion, it is unwise to eat, because the digestive organs are tired, and to load a tired stomach with food, still further weakens it and results in indigestion. The better plan is to drink two glasses of cold water and lie down for an hour; if there is still no desire for food, drink freely of water, but abstain from food until hungry.

This should not lead one into forming the habit of irregular eating, however. The stomach forms habits and the supply of food must be regular, just as the nursing child must be fed regularly, or digestive disturbance is sure to result.

A wise provision of Nature makes the system, in a normal condition, its own regulator, protesting against food when it has not assimilated or eliminated that consumed. One should learn to obey such protests and cut down the quantity when Nature calls “enough.”

There are exceptions, however. Some phases of indigestion result in a gnawing sensation in the stomach, which is often mistaken for a desire for food. This is not a normal appetite. Water will usually relieve it.

Often loss of appetite is the result of a clogging of intestines or liver, or to an excess of bile, which, not having been properly discharged into the intestines, has entered the blood stream. An excess of bile and poisons, indicating a torpid liver, often expresses itself in a dull mental force, the toxins deadening the nerve cells. Nature does not call for more food until she has eliminated the excess of waste.

It is commonly stated that the body will call for what the system requires. This may have been true of the aborigines, who ate their food in its natural state, and, to a certain extent, it is true to-day, but condiments and stimulants, to make the food “appetizing,” have unduly stimulated the nerves and perverted the natural taste; foods containing their natural amount of spices or extractives no longer tempt one. Those whose nerves are highly keyed, form the habit of seasoning the food too strongly, making it too stimulating. This undue stimulant calls for more food at the time of eating than a normal appetite would demand. The taste being cultivated for the stimulant, the habit of eating too much food is formed.

There is a difference between the cultivated and the normal appetite. A child rarely shows a desire for stimulants or condiments, unless unwisely encouraged by an adult, who does it,—_not because it is good for the child, but because the individual himself has cultivated a taste for it_. It is as easy to form healthful tastes and habits of eating as unhealthful ones, and care should especially be exercised in the formation of healthful habits by the growing child.

The simple foods, in their natural state, are in the right condition to be digested, with the aid of heat to break the cellular coverings of the globules of some of them, but time, energy, muscular activity, nerve force, and money are spent in combining, seasoning, and cooking foods in such a manner as often to render them difficult of digestion.

_Deep breathing of fresh air, to throw off the poisonous carbon dioxid and to supply an abundance of oxygen to oxidize the waste, thus putting it in condition to be expelled from the system; brisk exercise to accelerate the circulation, that the blood may carry the oxygen freely and that the tissues may liberate the carbon dioxid and other waste; and a copious drinking of water, are the best tonics for loss of appetite or for a lack of vitality._

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[Sidenote: Economy in Food]

It is economy, therefore, to keep the digestive organs and the circulation and tissues strong, in order that all foods eaten may yield returns, instead of hampering activity.

The food which furnishes the most tissue-building substance and yields the most heat and energy, with the least refuse, is the economical food. In the selection of food for any individual, the result to be gained from the food must be borne in mind. If one is doing heavy muscular work, more protein to rebuild tissue, as well as more carbohydrates and fats to produce energy, are required than if one’s habits of work are sedentary. In mental work, where the brain is continually active, proteins are required to re-supply the brain tissue, but the fats and carbohydrates may be lessened. This would seem to contradict the theory that where one’s habits are sedentary and the brain alone is active, the proteins are not required. In sedentary occupation, the carbohydrates and fats are stored within the system, clogging it and producing torpid liver, constipation, and obesity,—unless the brain is sufficiently active to use all of the fuel in brain energy.

In a dietary study of the following tables, the question should be to provide the largest quantity of nutriment at the lowest cost, with due attention to palatability and variety. In the selection of meats, for instances, while beefsteak may cost twice as much as beef stew, it must be borne in mind that beefsteak contains very little waste, and it contains a large proportion of albuminoids, or the tissue building proteins, while, in the beef stew, the bones and the connective tissue predominate; the proteins yielded from the beef stew are a large proportion gelatinoids and extractives,—not the tissue building albuminoids. This would not hold in comparing the cheaper and the more expensive cuts in the same kind of beefsteak; the cheaper cuts often yield quite as much nutriment as the more expensive ones. Round steak is just as nourishing as porter-house and much cheaper.

Much is said about the bacteria present in the atmosphere, the microbes in the food, etc., that one is puzzled to know, not only what to eat, but how to breathe, and, in fact, which way to turn to avoid them; but microbes and bacteria have been present in the atmosphere and in matter everywhere since time began. They are a part of the natural surroundings, and the body, if kept in strong vitality, has sufficient resistive power to enable one to live unharmed by them. The danger lies in allowing the system to run down and the vital force to ebb, so that the body becomes an easy prey to them.

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[Sidenote: Habit and Regularity of Eating.]

There is no doubt but that the _habit_ of eating governs one’s convictions of what the system requires. One is inclined to think that a desire for a food is a requirement of Nature; yet it may simply be the continuance of a habit. The vital organs form habits just as one forms a habit of walking, sitting or of carrying the head or the hands, and habit re-asserts itself.

If a mother feeds her babe every three hours the child will usually wake and call for food about this period. If she has formed the habit of nursing the child every two hours, it will call for food in about two hours, even though all symptoms indicate that the child is over fed.

It is important that both child and adult establish regular and hygienic habits because the digestive juices secrete themselves at the regular periods established. _A right habit is as easily formed, and as difficult to change, as a wrong one._

If one forms the habit of eating a certain amount of food, the stomach calls for about the same amount, and when one first begins to change the quantity it protests, whether the change be to eat more or less.

Few people form the habit of drinking sufficient water,—particularly if they have been taught that water at meals is injurious. In this busy life, few remember to stop work and drink water between meals, and if not consumed at the meal time the system suffers. Many people look “dried up.”

The habit of drinking two glasses of water upon first arising, and six more during the day is an important one.

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[Sidenote: Frequency of Meals]

There is no doubt but that a large number of people overload the digestive organs. This, as well as the bolting of food, insufficiently masticated, cannot be too strongly denounced. _All food should be chewed to a pulp before swallowed._

As a relief from overeating, many theorists are advocating two meals a day, but the work of the average man is planned into morning and afternoon sessions, and the three meals have been arranged accordingly.

Where two meals a day are eaten, the first meal should be at nine or ten o’clock in the morning and the second meal at five or six o’clock in the afternoon; whereas, for the average person who eats two meals a day, the custom is to go without food until the midday meal, and then to eat two meals within six hours, with nothing more for eighteen hours.

The argument in favor of two meals a day has been that the digestive system is inactive during sleep, and, therefore, the system is not ready for a meal upon arising, but the latest experiments (Pawlow) show that digestion continues during sleep, though less actively. It must be borne in mind that the average evening meal is eaten about six o’clock and that there are about four waking hours between this meal and the sleep period; also, that the average individual is awake and moderately active an hour before the morning meal. This gives five waking hours between the evening and the morning meal. About the same time, five hours, elapses between the morning and the midday meal, and between the midday and the evening meal, so that three meals a day divide the digestion periods about evenly.

More frequent meals, served in lighter quantity, with greater regularity, so that the system is not overloaded at any one meals, is rational for delicate, or undernourished nerves and tissues. The little child is fed regularly every three hours.

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[Sidenote: Effect of Exercise and Breathing upon Digestion]

Daily exercise and the habit of full breathing are absolutely necessary that the waste of the system may be fully liberated, that the nourishment may be carried freely to every tissue, and that sufficient oxygen may be carried through the blood to oxidize the waste, or, to put it into condition to be thrown off.

The necessity of oxygen as food is evident. The body will subsist about forty days upon the food stored within it, without re-supply, but it can endure only a few seconds without oxygen, because heat, occasioned by the union of oxygen with carbon and hydrogen, is necessary to keep up the physical activity termed “life.” _The necessity of habits of full, correct breathing cannot be too fully emphasized._ The quantity of oxygen, daily consumed, should fully equal the sum of all other food elements.[6]

Oxygen is necessary to cause combustion of fats, starches and sugars, just as it is necessary to cause combustion of carbon in wood, or coal.

The heat from “burning” wood is produced by the oxygen of the air uniting with hydrogen and carbon, forming carbon-dioxid (carbonic acid gas) and water.