772 THE FORMATION OF FAT. [BOOK u. 



condition however is temporary only, the lymph is subsequently 

 absorbed and the vesicle shrinks. At times, the emptying of the 

 cell, whether by the one method or the other, is followed by a 

 rejuvenescence of the cell, the nucleus by division gives rise to 

 several nuclei, and the cell divides into new cells, each of which 

 may, under appropriate conditions, develope again into a fat-cell. 



505. The fat thus lodged in adipose tissue varies somewhat 

 in composition in various animals, but is chiefly composed of 

 olein, palmitin and stearin in varying proportions, with small 

 quantities of the glycerin compounds of such fatty acids as butyric, 

 capronic, caprylic &c., together with a little lecithin and cholesterin. 

 The ' fat ' of one animal, that is the fat thus contained in adipose 

 tissue, differs from the fat of another animal partly by the presence 

 of more or less of one or more of these less abundant fats, but 

 chiefly by the proportion in which the three main fats, olein, 

 palmitin, and stearin, are respectively present in the mixed fat. 

 The melting points of these three fats being different, the melting 

 point of the fat of the body will differ according to the relative 

 proportions in which the three are present. Thus the subcu- 

 taneous fat of man melts at from 15 to 22 or higher, the fat 

 round the kidney being firmer and not melting until 25 ; the fat 

 of the dog melts at about 22, that of the goose at about 25, of 

 the ox at about 40, and of the sheep at 50, the less resistant fat 

 of the man and dog containing relatively more olein than that of 

 the ox or of the sheep. 



506. When we come to consider the question, By what 

 processes does the fat make its appearance in the fat-cell ? we are 

 brought face to face with much the same kind of problem as that 

 which occupied us in dealing with glycogen. On the one hand we 

 may suppose that the fat is brought to the fat-cell as fat and is in 

 some way taken up by the cell and deposited in the cell -substance 

 with little or no change. On the other hand, we may suppose that 

 the fat is manufactured by the fat-cell in some such way as mucin 

 or pepsin is manufactured by a mucous or a gastric cell, out of and 

 by means of its cell-substance, and that the process of fattening, or 

 of producing fat in fat-cells, consists essentially in feeding and so 

 building up the cell-substance which subsequently breaks down 

 into fat, and does not consist merely in bringing fat within reach 

 of the cell. Which of these views is the true one, or how far are 

 both these operations carried on in the animal body ? 



In support of the latter view it may be urged that, not only the 

 more complex living substance, but, as we have more than once 

 urged, the simpler proteid constituent of living substance obviously 

 contains what we may call a fatty radicle, so that we might expect 

 fat to be formed out of its metabolism. And as a matter of fact 

 not only in adipose tissue, but in every part of the body, living 

 substance is continuously giving rise to and temporarily depositing 

 in itself some amount of fat, and in what is known as fatty degen- 



