THE GENERAL NATURE OF DIET 137 



of various foods vary widely, however, in the degree of their respective 

 absorbability which is so essential. Atwater calculated from a large 

 amount of data that from a mixed diet the following proportions of 

 nutrient components are on the average absorbed : 



PERCENTAGES OF ABSORPTION. 



Another characteristic of foods is that they should require digestion. 

 This is on the universal principle that lack of exercise allows an organ 

 to degenerate. If the muscular and chemical arrangements of the 

 intestine are not employed actively they tend to lose their vigor. This 

 is the objection to the large use of partly predigested foods. 



THE GENERAL NATURE OF DIET. 



A diet is a selection of nutrients so arranged as to meet continuously 

 the requirements of an organism. This selection may be almost uncon- 

 scious, as was formerly that, for example, of an average farmer's family. 

 It may be, on the other hand, the exactly defined choice like that of the 

 army, or of a modern scientific research, like that, for instance, con- 

 ducted by the Department of Agriculture on the harmfulness of com- 

 mercial food-preservatives. The selection may be, in case of the 

 wealthy, from the whole artistic menu of the chef of a great hotel, or, 

 at the other logical extreme, in reality no choice at all, on which 

 basis was once the diet of potatoes of the Irish peasant and the rice of 

 the Chinese. Still, the leading notions in the term "diet" are those of 

 a set arrangement of nutrients for a considerable space of time, suffi- 

 cient, at least, to allow of observation of its effect, good or bad, general 

 or special, on an organism. 



Of the general requirements of a normal or ideal diet, so understood, 

 there are at least six which should be noted: (1) A diet must contain 

 both energizers and tissue-builders; (2) it must be sufficient in quantity 

 to support the organism in normal condition, but no larger in. amount; 

 (3) it must have the alimentary proximate principles or components in 

 nearly the proportions which best suit the needs of the organism ; (4) it 

 must contain a variety of nutrients both for each meal and from day to 

 day; (5) it must be adapted more or less accurately in a quantitative 

 way to the particular use of the organism under its specific conditions at 

 the time; (6) it must be adapted also qualitatively to the organism's 

 needs in certain physiological (and pathological) periods. 



A Source Both of Energy and of Tissue. Of the six alimentary com- 

 ponents already frequently mentioned (proteids, albuminoids, fats, 



