THE NUTRIENTS AND DIGESTION 313 



nitrogen may be made by the body into energy, heat, or fat. 

 This was demonstrated by Wolffberg and confirmed by Kulz 

 (as quoted by Lusk'), who showed in feeding fowls chopped 

 meat that part of the carbon of the protein was retained in 

 the body as glycogen (a carbohydrate of the liver). While 

 this is of interest it is not of great practical value, owing to 

 the fact that protein is the most expensive of the five food 

 nutrient groups and the tendency with most poultry feeders 

 is to slight the protein portion of the ration. 



Further Functions of the Nutrients. — Besides furnishing 

 material out of which the parts of the body and egg of the 

 same class are manufactured, as is also the case with ash 

 and water, the organic nutrients (protein, carbohydrates, and 

 fats) of the feed perform other services to the body. The 

 carbohydrates and fats are largely responsible for furnishing 

 the heat to maintain the normal body temperature and the 

 energy with wMch both voluntary and involuntary work is 

 performed. The waste tissue is repaired with protein and 

 the reproductive elements are largely protein. _ 



A summary of the uses of the nutrients is given below, 

 with the less important class placed in parentheses:^ 



Service Rendered. Classes. 



Supplying bodily heat. Carbohydrate and fat (protein) . 



Furnishing energy. Carbohydrate and fat (protein). 



Repairing waste tissue. Protein. 



Furnishing material for growth. Protein and ash. 



Reproduction. Protein (carbohydrate and fat) . 



Fattening. Carbohydrate and fat (protein). 



DIGESTION. 



Definition of Digestion. — Digestion is the process, accom- 

 plished by the crop, glandular stomach, gizzard, pancreas, 

 liver, and intestine, of so dissolving and chemically changing 

 the material taken into the alimentary tract that it can be 

 assimilated by the blood and used by the body. 



' Science of Nutrition. 



2 After Jaffa, California Bulletin No. 164. 



