
74 STORRS AGRICULTURAL EXPERIMENT STATION. 
THE NUTRIENTS OF FOOD. 
For the maintenance of life and activity the human machine 
requires material for the building and repair of its parts and 
for combustion to furnish heat and the energy required for 
external and internal muscular work. It is customary to 
classify the nutrients of the food into four groups—protein, 
fats, carbohydrates, and mineral matter or ash. 
PROTEIN—NITROGENOUS NUTRIENTS. 
The term protein is commonly applied to all the nitrogenous 
nutrients in the food with the exception of the nitrogenous 
fats. It includes a number of widely different groups of com- 
pounds with correspondingly different nutritive values. The 
protein compounds may be roughly divided into three groups. 
The first will include the most important of the nitrogenous 
nutrients, such as albumen of meat and egg, casein of milk, 
myosin of meat, gluten of wheat, etc., all of which are some- 
times grouped together as albuminoids. With these may be 
grouped also the so-called gelatinoids, such as chondrigen, 
gelatin, etc., derived from animal connective tissue. The 
members of this latter class are by some writers called pro- 
teids and by others albuminoids. Both of these classes are, 
in this article, grouped together as proteids. Distinguished 
from these are the third group, the non-proteids, including 
the creatin, creatinin and other so-called extractives of meat, 
and the amids, etc., of vegetable foods.* 
Sources and uses.—Protein is found in greater or less amounts 
in nearly all food materials, except the pure fats, sugars, and 
starches. The chief sources are meats, fish, eggs, and milk 
among the animal, and the legumes and cereals (beans and 
peas, wheat, corn, etc.) among the vegetable food materials. 
The garden vegetables and fruits furnish a very small amount 
of protein, and even this has a low nutritive value on account 
of its large proportion of non-proteids. ‘The protein of animal 
foods and the cereal grains is very largely composed of true 
proteids. Only these, and especially those here called albu- 
minoids as distinguished from the so-called gelatinoids, are 

* See discussion of this subject, with reference to authors, in U.S. Dept. Agr., Office 
of Experiment Stations, Bul. 65, p. 18. The terminology here emploved is that adopted 
provisionally by the Association of American Agricultural Colleges and Experiment 
Stations. 

