SUMMARY 339 



The unit for expressing food values in terms of heat is 

 the large Calorie which is the amount of heat necessary to 

 raise the temperature of 1000 grams of water 1 ° C. For many 

 purposes, however, this unit is not large enough for con- 

 venience and as a result the unit therm is now in use bv 



« 



Armsby. A therm is the quantity of heat necessary to raise 

 the temperature of 1000 kilograms of water 1° C, and it is 

 customary in expressing the value of food to do so as therms 

 per 100 pounds. 



241. Feeding Standards. — Ever since the functions of the 

 various food constituents in animal metabolism have been 

 known there has been a desire to determine scientifically the 

 amount of these constituents necessary for various classes 

 of animals and for various purposes. As a result we have 

 the so-called "feeding standards," which are based on 

 analytical and experimental data. The accurate obser- 

 vations of Armsby with his respiration calorimeter now make 

 it possible to establish standards which are reasonably 

 correct. Although even so, our knowledge is not by any 

 means perfect. The question of the proper feeding of stock, 

 and what should be more important the proper feeding of 

 man, is too large a one to be considered here. For further 

 information along this line the reader is directed to the 

 references given at the end of the chapter. 



242. Summary. — Food is defined as substances which 

 supply the body with material for its tissue, or with energy 

 for its activities. It is composed of various constituents, 

 each of which serves special functions and which requires 

 separate treatment in the animal body before being absorbed. 

 This process of solution of food constituents is called digestion 

 and takes place in the mouth, stomach, and small intestine. 



Salivary digestion is that which takes place in the mouth 

 where food is first ground up by the process of mastication. 

 Alkaline saliva is mixed with the food and the enzvme 

 ptyalin hydrolyzes starch to maltose. In the stomach where 

 gastric digestion takes place the food is mixed with the 

 acid gastric juice containing two enzymes: Pepsin, which 

 dissolves proteins to proteoses and peptones; and rennin, 

 which coagulates the caseinogen of milk, preparing it for 



