F\T Ml TABOLISM 70] 



It must no1 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 Btamp of individuality is pu1 upon the fat, for, 

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

 ing poinl changed during the process of absorption. In other woi 

 although the absorbed fal does no1 become entirely adapted to conform 

 with the ordinary qualities of the depot fat, ye1 it tends to change in 

 this direction. 



That sun f the depol fa1 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 museular exercise, its tias 

 become loaded with fat. It' we desire strict scientific proof for this, we 

 do not need to go further than the old experiments of Lawes and (!il- 

 bert, who, it will he remembered, showed thai the fat deposited in the 

 tissues of a growing pig is greatly in excess of the fat that could have 

 been derived from the fa1 or protein which was meanwhile metabolized. 

 The experiment was performed on two young pigs from the same lii 

 and of approximately equal weighl ; one was killed and the exacl amounts 

 of fat and nitrogen in the body determined; the other was fed for several 

 months on a diet the fat and protein contents of which were accurately 



ascertained. When after four months this p'n_ r was killed ami tin- fat 



determined, it was found that much more had 1m me deposited than 



could he accounted for by the fat and protein of the food, even Buppos- 

 ing that all the available carbon of the protein had become converted 



into fat. The only conclusion is thai the carbohydrate must have 1 n 



an important source of the extra fat. 



The Destination of the Depot Fat. The depol fat becomes mobilized 

 and transported by the blood to the active tissues whenever the energy 

 requirements of the body demand it. During starvation, as we have 

 seen, the depol fat is used to supply ! ,( > per cenl of the energy on which 



the animal maintains its existence. Before the fat is transported, il 



probably broken down into fatty acid ami glycerine, as which it pas 

 through the cell walls to he again reconstructed into neutral fat in I 



hi 1. What agency effects this constanl breakdown and resynthesis 



<>f fat it is difficull to say. Two ester-splitting enzymes are | -in 



blood, one acting mainly on simple esters, the other on glycerides; hut 



it has been impossible to demonstrate any evident relationship betw< 



either of them and the extent ..f t'at mobilization. 



The Fat in the Liver. The physiology of the liver fat has 1 n \> 



diligently studied, particularly by Leathes and his pupils. " Tin* out- 

 come of this work has hceii to buow that the liver upies an extremely 



important position in the melabolism of fat. being, as it were, the half- 



