COMPOSITION OF FOOD AND ACTION OF ENZYMES. 



677 



very much among themselves. Some idea of the limits of variation 

 may be obtained from the following table, taken chiefly from 

 Konig's analyses: 



The vegetable foods are distinguished, as a rule, by their large 

 percentage in carbohydrates and the relatively small amounts of 

 proteins and fats, as seen, for example, in the composition of rice, 

 corn, wheat, and potatoes. Nevertheless, it will be noticed that the 

 proportion of protein in some of the vegetables is not at all insignifi- 

 cant. They are characterized by their excess in carbohydrates 

 rather than by a deficiency in proteins. The composition of peas 

 and other leguminous foods is remarkable for the large percentage 

 of protein, which exceeds that found in meats. Analyses such as 

 are given here are indispensable in determining the true nutritive 

 value of foods. Nevertheless, it must be borne in mind that the 

 chemical composition of a food is not alone sufficient to determine 

 its precise value in nutrition. It is obviously true that it is not what 

 we eat, but what we digest and absorb, that is nutritious to the 

 body; so that, in addition to determining the proportion of food- 

 stuffs in any given food, it is necessary to determine to what extent 

 the several constituents are digested. This factor can be obtained 

 only by actual experiments. It may be said here, however, that 

 in general the proteins of animal foods are more completely digested 

 than are those of vegetables, and with them, therefore, chemical 

 analysis comes nearer to expressing directly the nutritive value. 



Accessory Articles of Diet. In addition to the foodstuffs 

 proper our foods contain numerous other substances which in one 

 way or another are useful in nutrition, although not absolutely 

 necessary. These substances, differing in nature and importance, 

 may be classified under the three heads of : 



Flavors : the various oils or esters that give odor and taste to foods. 

 Condiments: pepper, salt, mustard, etc. 

 Stimulants : alcohol, tea, coffee, cocoa, etc. 



The specific influence of these substances in digestion and nutrition 

 is considered in the section on nutrition. 



* Atwater: "The Chemistry of Foods and Nutrition," 1887. 



