FAT METABOLISM 705 



to act on unsaturated fatty acids in the cold, it causes hydroxyl groups to 

 be introduced in the position of the double bonds. When .the oxidation is 

 performed at a moderate temperature, the fatty acid falls apart at the 

 hydroxyl groups. A fatty acid with eight hydroxyl groups has been 

 obtained in this way from the liver of the pig. The presence of the hy- 

 droxyl groups has been confirmed by finding that an octobromide is ob- 

 tained by treatment with bromine. An acid of the same formula is said to 

 be present in cod-liver oil. To sum up, we may conclude that there are 

 certain positions, in the chains of carbon atoms which constitute the fatty- 

 acid radicle, where the liver introduces double bonds, and that the weak- 

 ened radicles then circulate to the tissues, where they break up at those 

 positions. 



But this is probably not the only way in which the liver assists in 

 the metabolism of fat. It may also take part in the building of fatty- 

 acid radicles into the complex molecule of lecithin. The process of de- 

 saturation that we have just considered is probably a preliminary step 

 to this incorporation of the fatty-acid molecule into lecithin, for it is 

 well known that lecithin contains highly unsaturated fatty-acid radi- 

 cles. In support of such a view it is interesting to note that in alcohol- 

 ether extracts from normal and pathologic livers, the lecithins, which are 

 precipitated by acetone, have higher iodine values (i. e., are more unsat- 

 urated) than the neutral fats extracted from the same liver, which also 

 have higher iodine values than the depot fat of the same animal. The 

 desaturation process must, therefore, involve the fatty acids before these 

 become built into the lecithin molecule. 



The liver is probably not the only place in the animal body where the 

 desaturation of fatty acids is brought about. The relative activity of 

 the different tissues in this regard has been studied by feeding cats 

 with fatty fish and then determining the iodine value of fat from various 

 places in the body. The absorbed fat was more obvious in the liver than 

 in the subcutaneous tissues, because it had not become diluted with fat 

 deposited it may have been months previously, which would be the 

 case in the fat of the fat depots; and it was found that, although the 

 iodine value of the subcutaneous fat was slightly raised, that of the 

 liver was much more so, indicating that the desaturation process had 

 been more active in this organ, but had also occurred to a certain extent 

 in the depots. 



Before leaving this subject of fat in the liver, it is important to re- 

 call the old observation of Rosenthal, that a more or less reciprocal 

 relationship exists between glycogen and fat in the liver. When much 

 glycogen is present there is little or no fat, and vice versa. It is impor- 



