one ton 1.54 feet. Atwater gives the following general estimate for the average amount of heat and energy in 1 pound of each of the classes of nutrients : 1 pound of protein..... 1 pound of fat.. 1 pound of carbohydrates ..1860 calories. .4220 66 66 Since the supply of food stuff or income must be regulated by the consumption or outgo, it is essential that the consumption should be determined. Experiments of this kind are made in an apparatus called the "Respiration Calorimeter," and include not only a quantitative analysis of the food, drink and air consumed by the man and of all the excretory products, which make up the income and outgo of the system, but also a careful estimate of the energy represented by ingested material as well as the energy liberated from the body in the various excreta, in heat and mechanical energy. The balance of income and expenditure is thus made, and the gain or loss of material of the body, with different kinds and amounts of food, and under different conditions of muscular exercise and rest, is determined. By means of these experiments, Prof. Atwater has been able to verify the law of the conservation of energy as applied to the animal. organism, and has shown that every unit of energy which enters the body as potential energy of the food will leave the body in potential energy as excreta, in heat radiated from the body, or in mechanical work done by the muscular system. The material income of the body must balance the material outgo and the energy income of the body must balance the energy outgo. According to the classical experiments of Pettenkoffer and Voit, nearly forty years ago, the waste products of a healthy adult weighing 154 pounds, during 24 hours, at rest amounted to 16.8 grams of nitrogen in the urine, 275 grams of carbon and 2,500 grams of water, while the waste products of the same individual, performing moderately hard muscular work, amounted to 18.8 grams of nitrogen, 328 of carbon and 2,190 grams of water, and from these experiments the authors named concluded that the following quantities of nutrients are required during 24 hours: Professor Chittenden's experiments, conducted about three years ago, indicate that the nitrogen equilibrium is preserved on a daily intake of 8.5 to 9.5 grams of nitrogen, or about 55 grams of nitrogenous food, so that the protein ration of Voit may be cut in two, provided the fats and carbohydrates are introduced in sufficient quantities to bring the full value up to 2,500 or 2,600 calories. Other authorities, however, believe that it would be unwise to reduce the protein ration below 100 grams or 3.5 ounces a day. One of the difficulties in the way of setting up exact standards is as pointed out by Professor Atwater, that "different individuals of the same class differ widely in their demands for food and in the use they make of it. Two men of like age, size, build and occupation may live and work side by side. One will eat more and the other less, while both do the same amount of work, or both may eat the same food and do the same work, and one will be fat and the other lean, or both may have the same diet and yet one will be strong and vigorous and able to do a great deal of work, while the other will be weak and able to accomplish but little. Just why individuals differ in their ways of utilizing their food and how to measure the differences and make dietary rules to fit them exactly, are problems which the physiological chemist has not yet solved." There are also persons who because of some peculiarity of the digestive system cannot use foods which for people in general are most wholesome and nutritious. Some persons cannot eat eggs, other suffer if they take milk, others have to avoid certain kinds of meat or fruit and all these indiosyncrasies indicate that the nutrition of man is not a mere matter of grams of protein, fats and carbohydrates. In fact we live not upon what we eat, but upon what we digest and assimilate. The whole subject of dietary standards is still in its infancy and the best we can do is to make estimates which apply to averages rather than individual cases. In a general way we may conclude that the needs of the economy are influenced (1) by the height and weight of the individual amounting to a difference of 40-50 calories for each kilogram in body weight; (2) by the temperament-nervous and excitable persons require more food than those of a phlegmatic temperament; (3) by muscular activity, which involves not only an increased expenditure of carbon, but also increased consumption of protein. (4) Age in so far as during active growth there is also a more active metabolism and children consume more for each kilogram of their weight than adults; on the other hand, with advancing years tissue metamorphosis becomes less active. (5) Sex influences the amount of tissue consumption only in so far as there is a difference in weight and muscular activity, an exception should be noted in pregnant and nursing women, who doubtless should receive a more liberal supply of proteids. (7) By temperature and climate. The influence of low temperatures results in increased oxidation of carbon, hence an instinctive craving for more fatty food and the carbohydrates, sugar and starches during the winter months and in cold climates. In the summer months and in warm climates there is a repugnance for fat and a craving for refreshing food and drinks, and hence the minimum amount of fat, about 40 grams and between 300 to 400 grams of carbohydrates with a normal protein ration will meet the requirements. Food stuffs are classified according to their proximate composition as follows: First: Organic, nitrogenous, as proteids or albuminoids; non-nitrogenous—a. fats, b. carbohydrates, c. vegetable acids. Second: Inorganic-mineral salts and water. Third: Food accessories, as tea, coffee and condiments. The first two classes of food stuff are essential to life, the third class is important as favoring palatability and digestibility. The true nutrients are protein, fats and carbohydrates. The term "protein" includes most of the nitrogenous food compounds, such as albuminoids, gelatinoids and extractives. 1. The albuminoids include all substances allied in their chemical composition to egg albumin, and have an average composition of N. 16%, C. 53%, H. 7%, O. 23%, S. 1%. They are found in eggs, lean part of meat, milk, curds and the gluten of wheat, the leguminous plants, etc. The principles of this group during digestion with the exception of nuclein are converted into soluble peptones or alkaline albuminates and readily absorbed as such; they are the chief tissue formers of the muscles and tendons of the body, but apart from this purely plastic function, they also play a role in oxidation and therefore in the generation of heat and energy. At all events they can take the place of fats and carbohydrates if the body has not enough of one or the other for fuel, but neither of the latter can take the place of albuminoids in building and repairing tissue. 2. The gelatinoids resemble the albuminoid group in their chemical composition; they are derived from ossein and chondrin (connective tissue) and are changed to gelatin on heating with water, and during digestion into gelatin-peptones. They are not tissue formers, but serve as fuel, and thus protect the protein fats and carbohydrates from consumption. Indeed 100 grams of gelatin can take the place of 36 grams of albumin and 25 grams of fat, but unfortunately large quantities are liable to cause nausea and diarrhea, probably because the undigested particles undergo rapid decomposition. 3. The extractives, so called because they are extracted from flesh by water, are known in the laboratory as creatin, creatinin, carnin, etc., and are the chief constituents of beef-tea and meat-extracts. Neither the extractives or amids found in vegetables like asparagus, betain, etc., can replace or exert a sparing effect on the consumption of albumin; they are therefore alimentary aids and not true foods. Indeed Kemmerich, over twenty years ago, pointed out that they are not free from danger on account of the large percentage of potassium salt; at all events, it has been shown that animals fed exclusively on meat extracts die more quickly from starvation than do those deprived entirely of food, and Fothergill, one of the most distinguished English foodexperts, expressed the opinion "that more lives have been lost by a mistaken belief in the food-value of beef-tea than by all the Napoleonic wars." Beef-tea acts as a regulator and stimulant of digestion and assimilation and like the meat-broths is useful in the dietary of sickness, provided we combine it with eggs, farinaceous food and small quantities of gelatin. The meat peptones and fluid meat, containing, as they do, considerable proportions of true nutriments, are much to be preferred but their nutritive value in the treatment of disease must not be overestimated. 4. The hydrocarbons of fats, whether derived from the animal or vegetable kingdom, are emulsified and saponified by the pancreatic juice and bile and finally reach the tissues where they become an integral part of the cells. Apart from aiding in the reconstruction of fatty tissues they undergo oxidation and thus supply heat and energy. Since the cells without exception contain more or less fat, it being, in conjunction with albumin, the principal constituent of nerve tissue, a store of adipose tissue, especially during febrile conditions, hard work or whenever the consumption exceeds the supply is very desirable. If the supply of fat exceeds the demand the excess is eliminated in the feces while other portions are stored up in the visceral cavities and subcutaneous tissues, where it serves as a non-conductor of heat, gives beauty and form to the body and protects various important structures from injury, but most important of all, if the supply should be cut off, or the consumption be increased, as during febrile conditions and hard work, this reserve fuel can be drawn upon for the production of heat and energy and thus protect the more important protein-compounds from oxidation. 5. The carbohydrates are non-nitrogenized principles which, in addition to carbon, contain hydrogen and oxygen in the proportion to form water. The formula for starch or dextrose is C.HO, and that of sucrose or cane sugar C12H22O11 10 5 The carbohydrates, whatever their source, enter the blood as sugar; normal blood contains about 0.1% and rarely more than 0.2% of sugar. The liver prevents a large accumulation by storing it up as glycogen or liver-starch, which under the influence of a peculiar ferment is re-converted into sugar as the needs of the economy demand, and any further excess is removed by the kidneys. The sugar in the blood is carried to the tissues, where it undergoes oxidation, yielding heat and energy. It is generally held that carbohydrates when ingested in liberal amounts may be converted into fat. How this is accomplished is not yet understood, but it may partly be accounted for by the fact that the oxidation of sugar saves the fatty and protein tissues from destruction and allows the fat in the diet to form new fatty tissues. 6. The pectin substances, like pectose and pectin, found in fruit and tubers, form jellies with water, are related to the carbohydrates and probably serve similar purposes in the economy. 7. The organic acids, like tartaric, mallic, citric, acetic, oxalic and lactic acids existing in fresh vegetables and fruits, fresh meats and milk, are transformed in the system into carbonates and as such preserve the alkalinity of the blood and other fluids. In the absence of these acids the blood becomes impoverished and scurvy is liable to develop. An excess is likely to interfere with digestion, especially with the conversion of starch into sugar, not to mention the laxative and diuretic properties. 8. The fact that 60% of the body is composed of water clearly indicates that a sufficient amount must be introduced to make up the loss sustained by its excretion through the lungs, kidneys, skin and feces. It is simply necessary to recall the physiological functions of water in the absorption and assimilation of food, the elimination of waste products, and its role as a heat regulator to appreciate that a deficiency is certain to be followed by injurious effects. 9. The mineral salts, which furnish about 6% of the body weight, are potassium, calcium, magnesium, sodium and iron in combination with chlorine, phosphoric, sulphuric and carbonic acid. The phosphates of lime, potash and magnesia contribute largely to the formation of bone, and are also essential for the growth of the nervous system. Iron is required for the red blood corpuscles and coloring matters, the chlorides are the source of hydrochloric acid in the gastric juice and keep the globulins of the blood and other fluids of the body in solution. Potassium for the blood cells and solid tissues and sodium for the intercellular fluids are all essential for the growth and repair of the tissues; of these certain quantities are daily eliminated and must be replaced. Forster has shown that when the supply in animals is suspended, serious digestive derange |