30 GENERAL FUNCTIONS OF THE ANIMAL BODY. 



circulating blood, by which they are transported and diffused 

 everywhere. 



4. Concerning the saline substances of the blood and other 

 animal fluids, and the phosphate of lime of the bones, I need 

 only add, that they exist in the plant in states of combination 

 more or less similar to those in which they are found in the 

 living fluids and tissues of the animal. 



Thus, while the plant has, to a certain extent, to deal with 

 the elementary bodies themselves, or with their more simple 

 combinations, and to bind them up into those compound mole- 

 cules of which its own parts consist, the animal begins with 

 these compounds, turns and alters them a little if necessary, and 

 at once fits them into their places. Each of the digestible con- 

 stituents of a plant serves its appointed purpose. The protein 

 compounds alone form muscle; the fat, sugar, &c., form the fat; 

 and the substance of the bones comes at once from the phos- 

 phates in the plant. 



This important general view must be our guide in all experi- 

 ments in feeding. It must be attended to equally by the 

 suggester, by the performer, and by the interpreter of such 

 experiments. 



6. General functions of the animal body. 



The general functions of the animal body must also be con- 

 sidered in all experiments upon cattle. The most important of 

 these functions are 



1. Respiration. The animal inhales atmospheric air, con- 

 taining only a small proportion two gallons in five thousand 

 of carbonic acid gas, and a little watery vapour. It expires 

 air loaded with watery vapour, and containing nearly a hundred 

 times as much carbonic acid three or four gallons in a hundred. 



The source and quantity of this carbonic acid are especially 

 important. It is composed of carbon and oxygen, of which 

 the former is derived from the food conveyed into the stomach, 

 the latter from the air inspired by the lungs. The quantity of 

 carbon thus thrown off from the lungs of a man varies from 

 five to thirteen ounces in the twenty-four hours. In the case 

 of the horse or the cow, it is five or six times as much ; and in 



