NOEMAL FAT METABOLISM 207 



largo amount (up to 15 per cent) in the cells of continuously active organs 

 like the heart and kidney as well as in lesser percentages in the muscles 

 furnish a basis for the theory that they constitute the form in which the 

 fats are utilized, and that food fat must undergo these changes desatura- 

 tion and phcsphorization before it can be utilized. The theory is given 

 support from the fact already discussed that whenever there occurs i\ 

 large accumulation of fat in the blood, most frequently in alimentary 

 lipemia, there is accompanying it a marked increase in the amount of 

 lipoid phosphorus present. 



The Liver in Fat Metabolism. That the liver plays an important 

 part in fat metabolism is indicated by the work of many investigators. 

 Munk (1902) found that the liver was loaded with fat during fat absorp- 

 tion. Leathes and Meyer- Wedell, by the use of a fat with high iodin num- 

 ber, found not only that the accumulated fat of the liver after feeding was 

 food fat but that the liver was the only organ in which such marked accu- 

 mulation occurred. In various abnormal conditions, such as poisoning with 

 phosphorus, chloroform or phloridzin, in diabetes, in starvation, etc., great 

 increases of the fat in the liver may occur which are believed to be the 

 result of mobilization of stored fat since the fat found in the liver at these 

 times has the properties of stored fat rather than of normal liver fat. 



The accumulations of fat in the liver whenever fat is being extensively 

 moved by the blood stream indicate that the liver must have an important 

 function in fat metabolism. Is it a temporary storehouse by means of 

 which the fat in the blood is kept within limits as is the case with the 

 carbohydrate, or does the fat undergo some essential change there? 

 Leathes' theory of the function of the liver in fat metabolism is that 

 mobilization of fat to' the liver is a normal process, that the fat is brought 

 there for two purposes: (a) introduction of double bonds (desaturation) 

 which paves the way for breaking the long fatty acid chains into shorter 

 ones, and (b) phosphorization of the fat, changing it into phospholipoids 

 which increasing evidence seems to show is the initial stage in the inter- 

 mediary metabolism of fat. The desaturation he believes to be specific for 

 the liver, but phosphorization may be accomplished in other places. His 

 theory is based on the following evidence: The fatty acids ordinarily 

 found in the liver differ from those of the stored fat in being much more 

 unsaturated. The liver is the only point of mobilization of fat from the 

 intestine or the fat stores. The inference is that the liver desaturates 

 the fatty acids which are brought to it. Since, however, similar un- 

 saturated fatty acids are found in other organs like the heart and kidney 

 it might with equal correctness be inferred that desaturation occurs in 

 these also. Some work by Mcttram with the plaice in which he found 

 that the fatty acids of the liver had a lower iodin number than those of 

 either the food or the muscles, would indicate that the liver may not always 

 have the function of desaturation. But as it is the only place where 



