CIRCULATION OF THE BLOOD. 195 



which will be governed very materially by the food and by 

 the perfection, the completeness, with which the fatty ele- 

 ments have been separated from the food, and enter into the 

 circulation of the blood. 



One animal may perform the first operation — the separa- 

 tion or elimination of the fatty matter in the food to be 

 stored away in the blood — as well as another, and, if so, 

 they accomplish the first step in the process of conversion 

 with equal economy ; and so far as this goes, — that is, the 

 separation and accumulation of fatty matter in the blood, 

 — it is the same whether the subsequent use to be made of 

 it be to form the fat or butter in milk, or the fat or tallow 

 of the body. 



Now, after this storing away of the fatty elements in the 

 blood, it will still depend largely upon the structure and 

 organism of the animal whether it will be deposited in the 

 form of fat, or secreted, — given up by the blood in the form 

 of the cream of milk. 



We see, therefore, that the economical preparation of the 

 raw material of the food is equally important for the fat in 

 the blood, whatever may be the ultimate form into which the 

 animal system is to convert it; and the internal structure 

 which accomplishes this process differs widely in different 

 individuals, so that one animal will effect this separation, 

 preparation, or elimination, completely, with the least possible 

 loss or waste of food ; while another will fail to e^ctract the 

 fatty elements of the food, and allow them to pass on to be 

 excreted with the other cast-off wastes of the body ; and we 

 see, also, that animals best formed for fattening are also best 

 formed to fulfil the first condition essential for the produc- 

 tion of rich milk. 



We have then arrived at the point where the fatty por- 

 tions of the food have entered into the circulation of the 

 blood, and are now to consider the influence of the living 

 animal system over these substances ; that is, the elimination 

 or secretion of either fat or milk. 



There are organs for the deposition of fat as well as for 

 the secretion of milk. The former are called adipose tissue ; 

 the latter, the mammary glands ; and whether these fatty 

 matters in the blood are to be changed, or deposited in the 

 form of the one or the other product, will depend mainly upon 



