What has resulted from artificial selection among dogs. (After Romanes.)
These discoveries of Mendel are of the greatest importance in plant and animal breeding because they enable the breeder to isolate certain characters and by proper selection to breed varieties which have these desired characters, instead of waiting for a chance union of the desired characters by nature.
Animal Breeding.—It has been pointed out that the domestication of wild animals, the horse, cattle, sheep, goats, and the dog, marked a great advance in civilization in the history of the earth's peoples. As the young of these animals came to be bred in captivity the peoples owning them would undoubtedly pick out the strongest and best of the offspring, killing off the others for food. Thus they came unconsciously to select and aid nature in producing a stronger and better stock. Later man began to recognize certain characters that he wished to have in horses, dogs, or cattle, and so by slow processes of breeding and "crossing" or hybridizing one nearly allied form with another the numerous groups of domesticated animals began to appear.
In Darwin's time animal breeding was so far advanced that he got his ideas of selection by nature in evolution from the artificial selection practiced by animal breeders. A glance at the pictures will give some idea of the changes that have taken place in the form of some animals since man began to breed them a few thousand years ago.
The four-toed ancestor of the present horse, restored from a study of its fossil skeleton. (After Knight in American Museum of Natural History.)
Some Domesticated Animals.—Our domesticated dogs are descended from a number of wolflike forms in various parts of the world. All the present races of cats, on the other hand, seem to be traced back to Egypt. Modern horses are first noted in Europe and Asia, but far older forms flourished on the earth in former geologic periods. It is interesting to note that America was the original home of the horse, although at the time of the earliest explorers the horse was unknown here, the wild horse of the Western plains having arisen from horses introduced by the Spaniards. Long ages ago, the first ancestors of the horse were probably little animals about the size of a fox. The earliest horse we have knowledge of had four toes on the fore and three toes on the hind foot. Thousands of years later we find a larger horse, the size of a sheep, with a three-toed foot. By gradual changes, caused by the tendency of the animals to vary and by the action of the surroundings upon the animal in preserving these variations, there was eventually produced our present horse, an animal with legs adapted for rapid locomotion, with feet particularly fitted for the life in open fields, and with teeth which serve well to seize and grind herbage. Knowledge of this sort was also used by Darwin to show that constant changes in the form of animals have been taking place since life began on the earth.
The horse, which for some reason disappeared in this country, continued to exist in Europe, and man, emerging from his early savage condition, began to make use of the animal. We know the horse was domesticated in early Biblical times, and that he soon became one of man's most valued servants. In more recent times, man has begun to change the horse by breeding for certain desired characteristics. In this manner have been established and improved the various types of horses familiar to us as draft horses, coach horses, hackneys, and the trotters.
It is needless to say that all the various domesticated animals have been tremendously changed in a similar manner since civilized man has come to live on the earth. When we realize the very great amount of money invested in domesticated animals; that there are over 60,000,000 each of sheep, cattle, and swine and over 20,000,000 horses owned in this country, then we may see how very important a part the domestic animals play in our lives.
Improvement of Man.—If the stock of domesticated animals can be improved, it is not unfair to ask if the health and vigor of the future generations of men and women on the earth might not be improved by applying to them the laws of selection. This improvement of the future race has a number of factors in which we as individuals may play a part. These are personal hygiene, selection of healthy mates, and the betterment of the environment.
Personal Hygiene.—In the first place, good health is the one greatest asset in life. We may be born with a poor bodily machine, but if we learn to recognize its defects and care for it properly, we may make it do its required work effectively. If certain muscles are poorly developed, then by proper exercise we may make them stronger. If our eyes have some defect, we can have it remedied by wearing glasses. If certain drugs or alcohol lower the efficiency of the machine, we can avoid their use. With proper care a poorly developed body may be improved and do effective work.
Eugenics.—When people marry there are certain things that the individual as well as the race should demand. The most important of these is freedom from germ diseases which might be handed down to the offspring. Tuberculosis, syphilis, that dread disease which cripples and kills hundreds of thousands of innocent children, epilepsy, and feeble-mindedness are handicaps which it is not only unfair but criminal to hand down to posterity. The science of being well born is called eugenics.
In this and the following diagrams the circle represents a female, the square a male. N means normal; F means feeble-minded; A, alcoholic; T, tubercular; Sx, sexually immoral; Sy, having syphilis. This chart shows the record of a certain family for three generations. A normal woman married an alcoholic and tubercular man. He must have been feeble-minded also as two of his children were born feeble-minded. One of these children married another feeble-minded woman, and of their five children two died in infancy and three were feeble-minded. (After Davenport.)
This chart shows that feeble-mindedness is a characteristic sure to be handed down in a family where it exists. The feeble-minded woman at the top left of the chart married twice. The first children from a normal father are all normal, but the other children from an alcoholic father are all feeble-minded. The right-hand side of the chart shows a terrible record of feeble-mindedness. Should feeble-minded people be allowed to marry? (After Davenport.)
The Jukes.—Studies have been made on a number of different families in this country, in which mental and moral defects were present in one or both of the original parents. The "Jukes" family is a notorious example. The first mother is known as "Margaret, the mother of criminals." In seventy-five years the progeny of the original generation has cost the state of New York over a million and a quarter of dollars, besides giving over to the care of prisons and asylums considerably over a hundred feeble-minded, alcoholic, immoral, or criminal persons. Another case recently studied is the "Kallikak" family.[35] This family has been traced back to the War of the Revolution, when a young soldier named Martin Kallikak seduced a feeble-minded girl. She had a feeble-minded son from whom there have been to the present time 480 descendants. Of these 33 were sexually immoral, 24 confirmed drunkards, 3 epileptics, and 143 feeble-minded. The man who started this terrible line of immorality and feeble-mindedness later married a normal Quaker girl. From this couple a line of 496 descendants have come, with no cases of feeble-mindedness. The evidence and the moral speak for themselves!
Parasitism and its Cost to Society.—Hundreds of families such as those described above exist to-day, spreading disease, immorality, and crime to all parts of this country. The cost to society of such families is very severe. Just as certain animals or plants become parasitic on other plants or animals, these families have become parasitic on society. They not only do harm to others by corrupting, stealing, or spreading disease, but they are actually protected and cared for by the state out of public money. Largely for them the poorhouse and the asylum exist. They take from society, but they give nothing in return. They are true parasites.
The Remedy.—If such people were lower animals, we would probably kill them off to prevent them from spreading. Humanity will not allow this, but we do have the remedy of separating the sexes in asylums or other places and in various ways preventing intermarriage and the possibilities of perpetuating such a low and degenerate race. Remedies of this sort have been tried successfully in Europe and are now meeting with success in this country.
Blood Tells.—Eugenics show us, on the other hand, in a study of the families in which are brilliant men and women, the fact that the descendants have received the good inheritance from their ancestors. The following, taken from Davenport's Heredity in Relation to Eugenics, illustrates how one family has been famous in American History.
In 1667 Elizabeth Tuttle, "of strong will, and of extreme intellectual vigor, married Richard Edwards of Hartford, Conn., a man of high repute and great erudition. From their one son descended another son, Jonathan Edwards, a noted divine, and president of Princeton College. Of the descendants of Jonathan Edwards much has been written; a brief catalogue must suffice: Jonathan Edwards, Jr., president of Union College; Timothy Dwight, president of Yale; Sereno Edwards Dwight, president of Hamilton College; Theodore Dwight Woolsey, for twenty-five years president of Yale College; Sarah, wife of Tapping Reeve, founder of Litchfield Law School, herself no mean lawyer; Daniel Tyler, a general in the Civil War and founder of the iron industries of North Alabama; Timothy Dwight, second, president of Yale University from 1886 to 1898; Theodore William Dwight, founder and for thirty-three years warden of Columbia Law School; Henrietta Frances, wife of Eli Whitney, inventor of the cotton gin, who, burning the midnight oil by the side of her ingenious husband, helped him to his enduring fame; Merrill Edwards Gates, president of Amherst College; Catherine Maria Sedgwick of graceful pen; Charles Sedgwick Minot, authority on biology and embryology in the Harvard Medical School; Edith Kermit Carow, wife of Theodore Roosevelt; and Winston Churchill, the author of Coniston and other well-known novels."
This record shows the inheritance of artistic ability (black circles and squares). (After Davenport.)
Of the daughters of Elizabeth Tuttle distinguished descendants also came. Robert Treat Paine, signer of the Declaration of Independence; Chief Justice of the United States Morrison R. Waite; Ulysses S. Grant and Grover Cleveland, presidents of the United States. These and many other prominent men and women can trace the characters which enabled them to occupy the positions of culture and learning they held back to Elizabeth Tuttle.
Euthenics.—Euthenics, the betterment of the environment, is another important factor in the production of a stronger race. The strongest physical characteristics may be ruined if the surroundings are unwholesome and unsanitary. The slums of a city are "at once symptom, effect, and cause of evil." A city which allows foul tenements, narrow streets, and crowded slums to exist will spend too much for police protection, for charity, and for hospitals.
Every improvement in surroundings means improvement of the chances of survival of the race. In the spring of 1913 the health department and street-cleaning department of the city of New York coöperated to bring about a "clean up" of all filth, dirt, and rubbish from the houses, streets, and vacant lots in that city. During the summer of 1913 the health department reported a smaller percentage of deaths of babies than ever before. We must draw our own conclusions. Clean streets and houses, clean milk and pure water, sanitary housing, and careful medical inspection all do their part in maintaining a low rate of illness and death, thus reacting upon the health of the citizens of the future. It will be the purpose of the following pages to show how we may best care for our own bodies and how we may better the environment in which we are placed.
[34] For full directions for budding and grafting, see Goff and Mayne, First Principles of Agriculture, Chap. XIX, Mayne and Hatch, High School Agriculture, pp. 159-165, or Hodge, Nature Study and Life, pages 169-179.
[35] The name Kallikak is fictitious.
Reference Books
elementary
Hunter, Laboratory Problems in Civic Biology. American Book Company.
Bailey, Plant Breeding. Macmillan and Company.
Harwood, New Creations in Plant Life. The Macmillan Company.
Jordan, The Heredity of Richard Roe. American Unitarian Association.
Sharpe, Laboratory Manual, pp. 64-72, 345-347. American Book Company.
advanced
Allen, Civics and Health. Ginn and Company.
Coulter, Castle, East, Tower, and Davenport, Heredity and Eugenics. University of Chicago Press.
Davenport, Heredity in Relation to Eugenics. Henry Holt and Company.
De Vries, Plant Breeding. Open Court Publishing Company.
Goddard, The Kallikak Family. The Macmillan Company.
Kellicott, The Social Direction of Human Evolution. Appleton Company.
Punnet, Mendelism. The Macmillan Company.
Richards, Helen M., Euthenics, the Science of Controllable Environment.
Walter, Genetics. The Macmillan Company.
Problem.—To obtain a general understanding of the parts and uses of the bodily machine.
Laboratory Suggestions
Demonstration.—Review to show that the human body is a complex of cells.
Laboratory demonstration by means of (a) human skeleton and (b) manikin to show the position and gross structure of the chief organs of man.
Man and his Environment.—In the last chapter we saw that one factor in the improvement of man lies in giving him better surroundings. It will be the purpose of the following chapters to show how man is fitted to live in the environment in which he is placed. He comes in contact with air, light, water, soil, food, and shelter which make his somewhat artificial environment; he must adapt himself to get the best he can out of this environment.
The Needs of Living Things.—We have already found that the primary needs of plants and animals are the same. They both need food, they both need to digest their food and to have it circulate in a fluid form to the cells where it will be used. They both need oxygen so as to release the energy locked up in their food. And they both need to reproduce so that their kind may be continued on the earth. What is true of plants and other animals is true of man.
The Needs of Simple and Complex Animals the Same.—The simplest animal, a single cell, has the same needs as the most complex. The cell paramœcium feeds, digests, oxidizes its food, and releases energy. The cells of the human body built up into tissues have the same needs and perform the same functions as the paramœcium. It is the cells of the body working together in groups as tissues and organs that make the complicated actions of man possible. Division of labor has arisen because of the complex needs and work of the organism.
The human body seen from the side in longitudinal section.
The Human Body a Machine.—In all animals, and the human animal is no exception, the body has been likened to a machine in that it turns over the latent or potential energy stored up in food into kinetic energy (mechanical work and heat), which is manifested when we perform work. One great difference exists between an engine and the human body. The engine uses fuel unlike the substance out of which it is made. The human body, on the other hand, uses for fuel the same substances out of which it is formed; it may, indeed, use part of its own substance for food. It must as well do more than purely mechanical work. The human organism must be so delicately adjusted to its surroundings that it will react in a ready manner to stimuli from without; it must be able to utilize its fuel (food) in the most economical manner; it must be fitted with machinery for transforming the energy received from food into various kinds of work; it must properly provide the machine with oxygen so that the fuel will be oxidized, and the products of oxidation must be carried away, as well as other waste materials which might harm the effectiveness of the machine. Most important of all, the human machine must be able to repair itself.
In order to understand better this complicated machine, the human body, let us briefly examine the structure of its parts and thus get a better idea of the interrelation of these parts and of their functions.
Skeleton of a man. CR., cranium; CL., clavicle; ST., sternum; H., humerus; V.C., vertebral column; R., radius; U., ulna; P., pelvic girdle; C., carpals; M., metacarpals; Ph., phalanges; F., femur; Fi., fibula; T., tibia; Tar., tarsals; MT., metatarsals.
The Skin.—Covering the body is a protective structure called the skin. Covered on the outside with dead cells, yet it is provided with delicate sense organs, which give us perception of touch, taste, smell, pressure, and temperature. It also aids in getting wastes out of the body by means of its sweat glands and plays an important part in equalizing the temperature of the body.
Bones and Muscles.—The body is built around a framework of bones. These bones, which are bound together by tough ligaments, fall naturally into two great groups, the bones of the body proper, vertebral column, ribs, breast bone, and skull, which form the axial skeleton, and the appendages, two sets of bones which form the framework of the arms and legs, which with the bones which attach them to the axial skeleton form the appendicular skeleton.
To the bones are attached the muscles of the body. Movement is accomplished by contraction of muscles, which are attached so as to cause the bones to act as levers. Bones also protect the nervous system and other delicate organs. They also help to give form and rigidity to the body.
Diagram showing action of biceps muscle. a, contracted; b, extended; h, humerus; s, scapula.
Hygiene of Muscles and Bones.—Young people especially need to know how to prevent certain defects which are largely the result of bad habits of posture. Standing erect is an example of a good habit, round shoulders a bad habit of this sort. The habit of a wrong position of bones and muscles once formed is very hard to correct. This can best be done by certain corrective exercises at home or in the gymnasium.
Round shoulders is most common among people whose occupation causes them to stoop. Drawing, writing, and a wrong position when at one's desk are among the causes. Exercises which strengthen the back muscles and cause the head to be kept erect are helpful in forming the habit of erect carriage.
Slight curvature of the spine either backward or forward is helped most by exercises which tend to straighten the body, such as stretching up with the hands above the head. Lateral curvature of the spine, too often caused by a "hunched-up" position at the school desk, may also be corrected by exercises which tend to lengthen the spinal column.
Three classes of levers in the human body; bones and muscles act together. A, a lever of the first class; B, a lever of the second class; C, a lever of the third class.
Bad posture in the schoolroom may cause permanent injury to the spine.
It is the duty of every girl and boy to have good posture and erect carriage, not only because of the better state of health which comes with it, but also because one's self-respect demands that each one of us makes the best of the gifts that nature has given us. An erect head, straight shoulders, and elastic carriage go far toward making their owner both liked and respected.
Other Body Structures.—In spaces between the muscles are found various other structures,—blood vessels, which carry blood to and from the great pumping station, the heart, and thence to all parts of the body; connective tissue, which holds groups of muscle or other cells together; fat cells, scattered in various parts of the body; various gland cells, which manufacture enzymes; and the cells of the nervous system, which aid in directing the body parts.
Body Cavity.—Within the body is a cavity, which in life is almost completely filled with various organs. A thin wall of muscle called the diaphragm divides the body cavity into two unequal spaces. In the upper space are found the heart and lungs, in the lower, the digestive tract with its glands, the liver, kidneys, and other structures (see page 267).
Digestion, Absorption, and Excretion.—Running through the body is a food tube in which undigested food is placed and from which digested or liquid food is absorbed into the blood so that the cells of the various organs which do the work may receive food. Emptying into this food tube are various groups of gland cells, which pour digestive fluids over the solid foods, thus aiding in changing them to liquids. Solid wastes are passed out through the posterior end of the food tube, while liquid wastes are excreted by means of glands called kidneys.
Work done by Cells.—Food, prepared in the digestive tract, and oxygen from the lungs are taken by the blood to the cells. Bathed in liquid food, the cells do their work; they promote the oxidization of food and the exchange of carbon dioxide for oxygen in the blood, while other wastes of the cells are given off, to pass eventually through the kidneys and out of the body.
The Nervous System.—The smooth working of the bodily machine is due to another set of structures which direct the working of the parts so that they will act in unison. This director is the nervous system. We have seen that, in the simplest of animals, one cell performs the functions necessary to its existence. In the more complex animals, where groups of cells form tissues, each having a different function, a nervous system is developed. The functions of the human nervous system are: (1) the providing of man with sensation, by means of which he gets in touch with the world about him; (2) the connecting of organs in different parts of the body so that they act as a united and harmonious whole; (3) the giving to the human being a will, a provision for thought. Coöperation in word and deed is the end attained. We are all familiar with examples of the coöperation of organs. You see food; the thought comes that it is good to eat; you reach out, take it, raise it to the mouth; the jaws move in response to your will; the food is chewed and swallowed. While digestion and absorption of the food are taking place, the nervous system is still in control. The nervous system also regulates pumping of blood over the body, respiration, secretion of glands, and, indeed, every bodily function. Man is the highest of all animals because of the extreme development of the nervous system. Man is the thinking animal, and as such is master of the earth.
Reference Reading for This and Succeeding Chapters on Human Biology
elementary
Hunter, Laboratory Problems in Civic Biology. American Book Company.
Davison, The Human Body and Health. American Book Company.
Gulick, The Gulick Hygiene Series. Ginn and Company.
Overton, General Hygiene. American Book Company.
Ritchie, Human Physiology. World Book Company.
Sharpe, Laboratory Manual in Botany, pages 218-225. American Book Company.
advanced
Halliburton, Kirk's Handbook of Physiology. P. Blakiston's Son and Company.
Hough and Sedgwick, The Human Mechanism. Ginn and Company.
Howell, Physiology, 3d edition. W. B. Saunders Company.
Schafer, Textbook of Physiology. The Macmillan Company.
Stiles, Nutritional Physiology. W. B. Saunders Company.
Verworn, General Physiology. The Macmillan Company.
Problems.—A study of foods to determine:—
(a) Their nutritive value.
(b) The relation of work, environment, age, sex, and digestibility of foods to diet.
(c) Their relative cheapness.
(d) The daily Calorie requirement.
(e) Food adulteration.
(f) The relation of alcohol to the human system.
Laboratory Suggestions
Laboratory exercise.—Composition of common foods. The series of food charts supplied by the United States Department of Agriculture makes an excellent basis for a laboratory exercise to determine common foods rich in (a) water, (b) starch, (c) sugar, (d) fats or oils, (e) protein, (f) salts, (g) refuse.
Demonstration.—Method of using bomb calorimeter.
Laboratory and home exercise.—To determine the best individual balanced dietary (using standard of Atwater, Chittenden, or Voit) as determined by the use of the 100-Calorie portion.
Demonstration.—Tests for some common adulterants.
Demonstration.—Effect of alcohol on protein, e.g. white of egg.
Demonstration.—Alcohol in some patent medicines.
Demonstration.—Patent medicines containing acetanilid. Determination of acetanilid.
Why we Need Food.—A locomotive engine takes coal, water, oxygen, from its environment. A living plant or animal takes organic food, water, and oxygen from its environment. Both the living and nonliving machine do[TN5] the same thing with this fuel or food. They oxidize it and release the energy in it. But the living organism in addition may use the food to repair parts that have broken down or even build new parts. Thus food may be defined as something that releases energy or that forms material for the growth or repair of the body of a plant or animal. The millions of cells of which the body is composed must be given material which will form more living matter or material which can be oxidized to release energy when muscle cells move, or gland cells secrete, or brain cells think.
The composition of milk. Why is it considered a good food?
Nutrients.—Certain nutrient materials form the basis of food of both plants and animals. These have been stated to be proteins (such as lean meat, eggs, the gluten of bread), carbohydrates (starches, sugars, gums, etc.), fats and oils (both animal and vegetable), mineral matter and water.
Proteins.—Protein substances contain the element nitrogen. Hence such foods are called nitrogenous foods. Man must form the protoplasm of his body (that is, the muscles, tendons, nervous system, blood corpuscles, the living parts of the bone and the skin, etc.) in part at least from nitrogenous food. Some of this he obtains by eating the flesh of animals, and some he obtains directly from plants (for example, peas and beans). Proteins are the only foods available for tissue building. They may be oxidized to release energy if occasion requires it.
Fats and Oils.—Fats and oils, both animal and vegetable, are the materials from which the body derives part of its energy. The chemical formula of a fat shows that, compared with other food substances, there is very little oxygen present; hence the greater capacity of this substance for uniting with oxygen. The rapid burning of fat compared with the slower combustion of a piece of meat or a piece of bread illustrates this. A pound of butter releases over twice as much energy to the body as does a pound of sugar or a pound of steak. Human fatty tissue is formed in part from fat eaten, but carbohydrate or even protein food may be changed and stored in the body as fat.
Carbohydrates.—We see that the carbohydrates, like the fats, contain carbon, hydrogen, and oxygen. Carbohydrates are essentially energy-producing foods. They are, however, of use in building up or repairing tissue. It is certainly true that in both plants and animals such foods pass directly, together with foods containing nitrogen, to repair waste in tissues, thus giving the needed proportion of carbon, oxygen, and hydrogen to unite with the nitrogen in forming the protoplasm of the body.
Three portions of foods, each of which furnishes about the same amount of nourishment.
Inorganic Foods.—Water forms a large part of almost every food substance. It forms about five sixths of a normal daily diet. The human body, by weight, is about two thirds water. About 90 per cent of the blood is water. Water is absolutely essential in passing off waste of the body. When we drink water, we take with it some of the inorganic salts used by the body in the making of bone and in the formation of protoplasm. Sodium chloride (table salt), an important part of the blood, is taken in as a flavoring upon our meats and vegetables. Phosphate of lime and potash are important factors in the formation of bone.
Phosphorus is a necessary substance for the making of living matter, milk, eggs, meat, whole wheat, and dried peas and beans containing small amounts of it. Iron also is an extremely important mineral, for it is used in the building of red blood cells. Meats, eggs, peas and beans, spinach, and prunes, are foods containing some iron.
Some other salts, compounds of calcium, magnesium, potassium, and phosphorus, have been recently found to aid the body in many of its most important functions. The beating of the heart, the contraction of muscles, and the ability of the nerves to do their work appear to be due to the presence of minute quantities of these salts in the body.
Uses of Nutrients.—The following table sums up the uses of nutrients to man:[36]—
| Protein | Forms tissue | |
| White of eggs (albumen), curd of milk (casein), lean meat, gluten of wheat, etc. | (muscles, tendon, and probably fat) | |
| Fats | Form fatty tissue. | |
| Fat of meat, butter, olive oil, oils of corn and wheat, etc. | All serve as fuel and yield energy in form of heat and muscular strength. | |
| Carbohydrates | Transformed into fat. | |
| Sugar, starch, etc. | ||
| Mineral matters (ash) | Aid in forming bone, | |
| Phosphates of lime, potash, soda, etc. | assist in digestion, aid in absorption and in other ways help the body parts do their work. | |
| Water used as a vehicle to carry nutrients, and enters into the composition of living matter. | ||
Common Foods contain the Nutrients.—We have already found in our plant study that various plant foods are rich in different nutrients, carbohydrates forming the chief nutrient in the foods we call cereals, breads, cake, fleshy fruits, sugars, jellies, and the like. Fats and oils are most largely found in nuts and some grains. Animal foods are our chief supply of protein. White of egg and lean meat are almost pure protein and water. Proteins are most abundant, as we should expect, in those plants which are richly supplied with nitrogen; peas and beans, and in grains and nuts. Fats, which are melted into oils at the temperature of the body, are represented by the fat in meats, bacon, pork, lard, butter, and vegetable oils.
Water.—Water is, as we have seen, a valuable part of food. It makes up a very high percentage of fresh fruits and vegetables; it is also present in milk and eggs, less abundant in meats and fish, and is lowest in dried foods and nuts. The amount of water in a given food is often a decided factor in the cost of the given food, as can easily be seen by reference to the chart on page 283.
Table of food values. Determine the percentage of water in codfish, loin of beef, milk, potatoes. Percentage of refuse in leg of mutton, codfish, eggs, and potatoes. What is the refuse in each case? Find three foods containing a high percentage of protein; of fat; of carbohydrate. Find some food in which the proportions of protein, fat, and carbohydrate are combined in a good proportion.
Refuse.—Some foods bought in the market may contain a certain unusable portion. This we call refuse. Examples of refuse are bones in meat, shells of eggs or of shellfish, the covering of plant cells which form the skins of potatoes or other vegetables. The amount of refuse present also plays an important part in the values of foods for the table. The table[37] on page 276 gives the percentages of organic nutrients, water, and refuse present in some common foods.
Fuel Values of Nutrients.—In experiments performed by Professor Atwater and others, and in the appended tables, the value of food as a source of energy is stated in heat units called Calories. A Calorie is the amount of heat required to raise the temperature of one kilogram of water from zero to one degree Centigrade. This is about equivalent to raising one pound four degrees Fahrenheit. The fuel value of different foods may be computed in a definite manner. This is done by burning a given portion of a food (say one gram) in the apparatus known as a calorimeter. By this means may be determined the number of degrees the temperature of a given amount of water is raised during the process of burning. It has thus been found that a gram of fat will liberate 9.3 Calories of heat, while a gram of starch or sugar only about 4 Calories. The burning value of fat is, therefore, over twice that of carbohydrates. In a similar manner protein has been shown to have about the same fuel value as carbohydrates, i.e. 4 Calories to a gram.[38]
The Relation of Work to Diet.—It has been shown experimentally that a man doing hard, muscular work needs more food than a person doing light work. The mere exercise gives the individual a hearty appetite; he eats more and needs more of all kinds of food than a man or boy doing light work. Especially is it true that the person of sedentary habits, who does brain work, should be careful to eat less food and food that will digest easily. His protein food should also be reduced. Rich or hearty foods may be left for the man who is doing hard manual labor out of doors, for any extra work put on the digestive organs takes away just so much from the ability of the brain to do its work.
Foods of plant origin. Select 5 foods containing a high percentage of protein, 5 with a high percentage of carbohydrates, 5 with a high percentage of water. Do vegetable foods contain much fat? Which of the above-mentioned foods have the highest burning value?
Foods largely of animal origin. Compare with the previous chart with reference to amount of protein, carbohydrate, and fat in foods. Compare the burning value of plant and animal foods. Compare the relative percentage of water in both kinds of foods.
The composition of milk.
The Relation of Environment to Diet.—We are all aware of the fact that the body seems to crave more food in winter than in summer. The temperature of the body is maintained at 98.6° in winter as in summer, but much more heat is lost from the body in cold weather. Hence feeding in winter should be for the purpose of maintaining our fuel supply. We need heat-producing food, and we need more food in winter than in summer. We may use carbohydrates for this purpose, as they are economical and digestible. The inhabitants of cold countries get their heat-releasing foods largely from fats. In tropical countries and in hot weather little protein should be eaten and a considerable amount of fresh fruit used.
The Relation of Age to Diet.—As we will see a little later, age is a factor not only in determining the kind but the amount of food to be used. Young children require far less food than do those of older growth or adults. The body constantly increases in weight until young manhood, or womanhood, then its weight remains nearly stationary, varying with health or illness. It is evident that food in adults simply repairs the waste of cells and is used to supply energy. Elderly people need much less protein than do younger persons. But inasmuch as the amount of food to be taken into the body should be in proportion to the body weight, it is also evident that growing children do not, as is popularly supposed, need as much food as grown-ups.
The Relation of Sex to Diet.—As a rule boys need more food than girls, and men than women. This seems to be due to, first, the more active muscular life of the man and, secondly, to the greater amount of fat in the tissues of the woman, making loss of heat less. Larger bodies, because of greater surface, give off more heat than smaller ones. Men are usually larger in bulk than are women,—another reason for more food in their case.
The Relation of Digestibility to Diet.—Animal foods in general may be said to be more completely digested within the body than plant foods. This is largely due to the fact that plant cells have woody walls that the digestive juices cannot act upon. Cereals and legumes are less digestible foods than are dairy products, meat, or fish. This does not mean necessarily that these foods would not agree with you or me but that in general the body would get less nourishment out of the total amount available.
The agreement or disagreement of food with an individual is largely a personal matter. I, for example, cannot eat raw tomatoes without suffering from indigestion, while some one else can digest tomatoes but not strawberries. Each individual should learn early in life the foods that disagree with him personally and leave such foods out of his dietary. For "what is one man's meat may be another man's poison."
The Relation of Cost of Food to Diet.—It is a mistaken notion that the best foods are always the most expensive. A glance at the table (page 283) will show us that both fuel value and tissue-building value is present in some foods from vegetable sources, as well as in those from animal sources, and that the vegetable foods are much cheaper. The American people are far less economical in their purchase of food than most other nations. Nearly one half of the total income of the average workingman is spent on food. Not only does he spend a large amount on food, but he wastes money in purchasing the wrong kinds of food. A comparison of the daily diets of persons in various occupations in this and other countries shows that as a rule we eat more than is necessary to supply the necessary fuel and repair, and that our workingmen eat more than those of other countries. Another waste of money by the American is in the false notion that a large proportion of the daily dietary should be meat. Many people think that the most expensive cuts of meat are the most nutritious. The falsity of this idea may be seen by a careful study of the tables on pages 283 and 286.
The Best Dietary.—Inasmuch as all living substance contains nitrogen, it is evident that protein food must form a part of the dietary; but protein alone is not usable. If more protein is eaten than the body requires, then immediately the liver and kidneys have to work overtime to get rid of the excess of protein which forms a poisonous waste harmful to the body. We must take foods that will give us, as nearly as possible, the proportion of the different chemical elements as they are contained in protoplasm. It has been found, as a result of studies of Atwater and others, that a man who does muscular work requires a little less than one quarter of a pound of protein, the same amount of fat, and about one pound of carbohydrate to provide for the growth, waste, and repair of the body and the energy used up in one day.
The Daily Calorie Requirement.—Put in another way, Atwater's standard for a man at light exercise is food enough to yield 2816 Calories; of these, 410 Calories are from protein, 930 Calories from fat, and 1476 Calories from carbohydrate. That is, for every 100 Calories furnished by the food, 14 are from protein, 32 from fat, and 54 from carbohydrate. In exact numbers, the day's ration as advocated by Atwater would contain about 100 grams or 3.7 ounces protein, 100 grams or 3.7 ounces fat, and 360 grams or 13 ounces carbohydrate. Professor Chittenden of Yale University, another food expert, thinks we need proteins, fats, and carbohydrates in about the proportion of 1 to 3 to 6, thus differing from Atwater in giving less protein in proportion. Chittenden's standard for the same man is food to yield a total of 2360 Calories, of which protein furnishes 236 Calories, fat 708 Calories, and carbohydrates 1416 Calories. For every 100 Calories furnished by the food, 10 are from protein, 30 from fat, 60 from carbohydrate. In actual amount the Chittenden diet would contain 2.16 ounces protein, 2.83 ounces fat, and 13 ounces carbohydrate. A German named Voit gives as ideal 25 Calories from proteins, 20 from fat, and 55 from carbohydrate, out of every 100 Calories; this is nearer our actual daily ration. In addition, an ounce of salt and nearly one hundred ounces of water are used in a day.