PROTEIDS. 127 



From the above consideration of the food-stuffs it is seen that 

 they are in most respects the same as the tissues of the body ; yet 

 it would be erroneous to infer that the fats and the proteids of the 

 food go directly into the tissues as such, and take the place of the 

 fats and the proteids which are wasted. There are many inter- 

 mediate steps, some of which are known and will be discussed, 

 and others of which we are entirely ignorant. Experience has 

 abundantly demonstrated that in order to maintain the body at 

 its physiologic standard representatives from all these four classes 

 of food-stuffs must be supplied. If man is deprived of water, 

 death speedily results ; it comes as surely, though not so quickly, 

 if fats or carbohydrates or proteids are cut off from the food- 

 supply. Indeed, a man may be starved to death by withholding 

 the salts. 



Whenever, therefore, it is found that life can be maintained 

 physiologically for a long period of time on any diet, it is certain 

 that this diet contains representatives of all the classes enumer- 

 ated. Thus, milk, which is the sole food of young children 

 among some of the Eskimos to the sixth year of life is found on 

 analysis to contain such representatives ; the inorganic class being 

 represented by water and salts, the carbohydrates by milk-sugar, 

 the fats by butter, and the proteids by caseinogen, lactalbumin, and 

 lactoglobulin. It is not, however, sufficient that each class should 

 be represented, but the proportions of the ingredients must be proper. 

 It is possible that any given food may have the requisite constituents, 

 but may have too much of one and too little of another. It has been 

 determined that the daily waste of the body is 250 to 280 grams 

 of carbon and 15 to 18 grams of nitrogen, or about 16 to 1. The 

 carbon given off is principally in the form of carbonic acid in the 

 expired air, while the urea of the urine contains most of the 

 nitrogen eliminated. To supply the waste of the body, then, the 

 proportion in the food of carbon to nitrogen should be as 16 to 1. 



In proteids, however, the proportion is 3.5 to 1, so that should 

 proteids only be supplied to the body there would have to be given 

 an enormous amount of nitrogenous food in order to supply enough 

 of the carbonaceous. The effect of this excess of nitrogenous 

 food would be to injure the digestive and eliminating organs. So 

 that to make up this deficiency of carbon, carbohydrates and fats 

 are used in connection with the proteids. Imagine, for instance, 

 the effect upon the digestive apparatus if man's exclusive diet 

 was potatoes. It will be seen by the table that in potatoes there 

 are 2 per cent, of proteids and 20.75 per cent, of carbohydrates. 

 Therefore, to obtain enough proteids from potatoes to sustain life 

 it would be necessary to eat daily at least 3.37 kilograms, or twenty- 

 five good-sized potatoes. In some parts of the world this has been 

 put into practice, the effect being to distend the stomach and to 

 derange digestion to a harmful degree. 



And yet we must acknowledge that human life is sustained for 



