So AGRICULTURE. [en. 



their habits of life, and in their constitutional character, 

 from the original breeds from which they were obtained. 

 These variations must however be regarded as unna- 

 tural and abnormal conditions, and as being obtained 

 for the more economical production of meat. We 

 cannot run contrary to the course of nature, yet, like 

 mariners who have adverse winds to deal with, we can 

 "tack about," so as to be carried forward by the 

 functions of animal life, to the attainment of a result 

 totally different from that which the same agencies 

 would have produced, had the animal existed in a 

 wild condition. 



166. Fat is produced from the non-nitrogenous 

 portions of the animal's food, and its chief use in the 

 animal body is to maintain the heat of the body. 

 The temperature of the animal body is higher than 

 the air in which it usually lives. An ox has a body- 

 heat of 100 Fahr., and for its healthy condition this 

 temperature should be maintained. If there were no 

 internal source of heat, the warmth of the body would 

 fall to that of the surrounding air, and this does take 

 place after death. The lungs of the animal assist 

 largely in this very important duty. The oxygen of 

 the atmosphere being drawn into the lungs, is thus 

 enabled to act upon the non-nitrogenous matters 

 which are in the blood. These matters contain a 

 large quantity of carbon, and by the union of the 

 oxygen of the air with the carbon of the food, we 

 have carbonic acid formed. The animal therefore 

 draws in oxygen, and throws off carbonic acid. The 

 lungs thereby do the work of a pair of bellows, and by 

 the addition of oxygen to the blood the carbon is gradu- 

 ally burnt off or oxidized, as the blood is circulating 

 through the body of the animal. The following analysis 

 of atmospheric air and the breath of an animal, given by 

 Playfair, will sufficiently illustrate this fact : 



