606 THE FORMATION OF FAT. [Book ii. 



by fat becomes filled with a clear fluid resembling lymph, the 

 fat vesicle being transformed into a lymph vesicle. This con- 

 dition however is temporary only, the lymph is subsequently 

 absorbed and the vesicle shrinks. Or the cell-substance may 

 shrink round the lessening fat, but in doing so deposits on its 

 outside a mucous substance. 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. 



S 399. The fat thus lodged in adipose tissue varies some- 

 what in composition in various animals, but is chiefly composed 

 of olein, palmitin and stearin in varying proportions, with small 

 quantities of the glycerine 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 con- 

 tained 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 subcutaneous 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. 



§ 400. 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 



