730 



METABOLISM 



The Depot Fat 



The places in the animal body where depot fat is deposited in great- 

 est amount are the subcutaneous and retroperitoneal tissues. These 

 fat depots may sometimes become of enormous size, as in the case of 

 the famous dog of Pfliiger, of whose total body weight 40 per cent was 

 due to fat. Bloor suggests that there may really be two different types 

 of fat storage : one of a purely temporary character, which readily 

 takes up and liberates the fat, but which is of limited capacity and 

 possibly under the control of some quickly acting regulating mech- 

 anism, like that of the glycogenic function of the liver; and another 

 of a more permanent nature, into which the fat is slowly taken up, but 

 the capacity of which is very much greater. 



Two questions present themselves concerning the depot fat: (1) where 

 does it come from, and (2) what becomes of it? Regarding the source 

 of the depot fat, there is no doubt that it comes partly from the fat and 

 partly from the carbohydrate of the food; in other words, it is either 

 taken ready-made with the food or manufactured in the organism. That 

 some of it comes from the fat of food is now a well-established fact, the 

 evidence for which need not detain us long. The best-known experiment 

 consists in first of all starving an animal until its stores of fat are 

 nearly exhausted and then feeding it with some "ear-marked" fat- 

 that is, with some fat having a characteristic property which it will 

 not lose during absorption. It will be found that the depot fat thereby 

 deposited presents many of the qualities of the fed fat. The "ear- 

 marking" of the fat may be secured by using fats of different melting 

 points, such as mutton fat, which has a high M.P., or olive oil, which has 

 a low M.P. On feeding a previously starved dog with mutton fat, the 

 M.P. of the depot fat approaches that of mutton fat he becomes a 

 dog in sheep's clothing; whereas when olive oil is fed, the subcutaneous 

 fat becomes oily. Or again we may "ear-mark" the fat by combining it 

 with bromine, when the deposited fat will likewise be brominized fat. 



It must not be imagined, however, that no change takes place in the 

 fat during its absorption and before it becomes deposited in the tissues. 

 On the contrary, the stamp of individuality is put upon the fat, for, as 

 we have already seen, its iodine value may become altered and its melt- 

 ing point changed during the process of absorption. In other words, 

 although the absorbed fat does not become entirely adapted to conform 

 with the ordinary qualities of the depot fat, yet it tends to change in 

 this direction. 



That some of the depot fat comes from carbohydrate is well known to 

 stock raisers. When, for example, an animal is fed on large quantities 

 of carbohydrate and kept without doing muscular exercise, its tissues 



