90 ELEMENTARY BIOLOGY 



discovering useful food plants and food animals that are stran- 

 gers to us but familiar to people in remote parts of the earth, 

 and neither our instincts nor our customs tell us the best way 

 to use them. Even in regard to the older kinds of food we are 

 almost as ignorant ; for while we know that the flesh of an ox 

 is better for food than the hoof or the hide, and that the grain 

 of the wheat is better than the leaf or the root, experience has 

 not taught us what proportions of meat and grain and fruit are 

 the best for maintaining efficient health, and certainly we have 

 to learn that one combination of foods is best for one person, 

 while another combination is best for another person. 



127. Dietary studies. When the study of dietaries was first 

 begun, it was assumed that what people actually eat is on the 

 average the best thing for them to eat, both as to kind and as 

 to quantitv. Accordingly students made careful records of the 

 meat and bread and butter and vegetables and fruits and cheese 

 eaten by thousands of people. They calculated the amount of 

 protein, fat, and carbohydrates contained in these dietaries, 

 and sought thus to establish, from the averages, a standard 

 of what healthy people require day by day. By this method 

 Carl Voit in Germany and Professor W. O. Atwater in this 

 country concluded that a person doing a moderate amount of 

 work needs about four ounces of protein daily, to take the 

 place of the proteins oxidized in the cells of the body. But 

 later experiments, in which the amount of protein taken in 

 and the amount of nitrogenous waste given off were carefully 

 measured, lead to the conclusion that an adult weighing about 

 one hundred and sixty pounds requires hardly more than two 

 ounces of proteins in every twenty-four hours. 



Since protein is the most expensive material in our food, and at the 

 same time the one that is most severe upon the organs of the body, 

 especially the liver and kidneys, it is a matter of great importance to 

 know whether two ounces will suffice or whether four ounces are 

 necessary. We should therefore try to understand the basis upon 

 which these diverse standards are established. 



