364 A MANUAL OF VETERINARY PHYSIOLOGY 



The loss in the glandular organs was very heavy ; next followed 

 the muscles, and then the blood. The heart muscle and central 

 nervous system suffered no loss ; evidently their nutrition was 

 kept up at the expense of other tissues of less importance. Old 

 animals bear starvation much better than young growing ones, 

 as their requirements are smaller. 



Cause of Body Waste. — The work of the body may be described 

 as internal and external. By internal work we refer to respira- 

 tion, the action of the heart, mastication, peristalsis, glandular 

 secretion, hydrolysis, fermentation, warming of ingesta, cleavage 

 and synthesis during absorption, the production of animal heat, 

 all of which are sources of expenditure of energy ; by external 

 work is understood those movements of the muscles which sup- 

 port or transport the body. Every diet given to an animal must 

 take these two factors into consideration. The ration of sub- 

 sistence is the minimum diet necessary for the internal work of 

 the body without incurring loss of weight, the animal, of course, 

 doing no work ; the ration of labour furnishes the actual muscular 

 energy employed during work. The changes undergone by food 

 in providing energy as heat and motion fall principally, if not 

 exclusively, on the non-nitrogenous elements. This has been 

 settled beyond all doubt. 



During work the heart and respirations are quickened, the 

 horse sweats, and a larger volume of air is warmed in the lungs. 

 All this means a loss of heat to the body. In addition, the 

 muscles produce heat as the result of contraction — in fact, every 

 process seems to tell essentially on the non-nitrogenous elements 

 of the body, which is the explanation why carbohydrates are so 

 necessary. 



The Energy yielded by Food has been ascertained by burning 

 the substance in a calorimeter and measuring the amount 

 -of heat given off. In this way the potential energy of 

 protein, fat, and carbohydrate has been ascertained. Every 

 1 gramme (15*432 grains) of water in the calorimeter raised i°C. 

 (i-8° F.) is called a heat unit; by this method of investigation 

 it has been found that — ■ 



1 gramme of average protein evolves, approximately, when oxi- 

 dised, 5,770 heat units,* or 5-7 large calories. f 



1 gramme of fat evolves, when oxidised, 9,300 heat units, or 

 9' 3 large calories. 



1 gramme of carbohydrate evolves, when oxidised, 4,100 heat 

 units, or 4- 1 large calories. 



* One heat unit or small calorie is the quantity of heat necessary to 

 raise 1 gramme of water 1 ° C. in temperature, 

 f For definition see footnote, p. 358. 



