RESPIRATORY FOOD. 43 



food takes place in the cells and the capillaries of the body 

 instead of the lungs, and that animal heat is thus generated 

 all over the "body. This shows the same necessity for car- 

 bonaceous food as the first theory, and as this effete matter 

 from the combustion of the carbon in the cells and capil- 

 laries is constantly thrown off at the lungs, it may, al- 

 though not strictly correct, be called the food of respiration. 



Here, then, we find one important use for starch, gum, 

 and sugar in food ; these being composed entirely of 

 carbon and water, are so simple in combination that the 

 carbon is easily separated, and therefore are admirably 

 adapted to generate animal heat. If the food is de- 

 ficient in starch, gum, or sugar, but contains fat, then 

 fat is used to supply carbon. Albuminoids also contain 

 carbon; and when there is no other resource for this 

 element of combustion, albuminoids are decomposed to 

 supply the carbon required ; but herbivorous animals 

 do not thrive when fed wholly upon nitrogenous food. 

 For this reason, foods very rich in albuminoids should 

 not be fed alone that is peas, or oil-meal should always 

 be mixed with hay, straw, turnips, or other roots rich 

 in starch, sugar, etc. Fatty substances differ from starch, 

 gum, and sugar, simply in containing more hydrogen 

 than is necessary to form water with the oxygen present. 

 Fatty matters are thus not so easily decomposed to furnish 

 the necessary carbon as the starchy compounds. 



It becomes evident from the points discussed, that the 

 health of animals cannot be sustained without a mixed 

 diet ; that the food given in order to keep the animal in 

 health must contain : 1. Starch, gum, sugar, or cellulose, 

 to supply the carbon given off in respiration. 2. Fat, or 

 fatty oil, to supply the fatty matter which exists in all 

 animal bodies. 3. Gluten, albumen, legumen, or casein, 

 to make up for the natural waste of the muscles and car- 

 tilages, and to grow this part of the system of the young 



