732 METABOLISM 



tains much potential energy, but not in a suitable condition for explo- 

 sion. The liver, as it were, dries this gunpowder, whence it is sent to 

 the tissues to be exploded. 



The great importance of the liver in fat metabolism is indicated by 

 comparison of the percentages of fat or better of fatty acid contained 

 in it under different conditions of nutrition. In the ordinary run of 

 slaughter-house animals the liver contains from 2 to 4 per cent of higher 

 fatty acid, but in about one in every eight animals a much higher per- 

 centage will be found to occur. The same is true in laboratory animals. 

 In the case of the human liver as obtained from autopsies in certain 

 classes of patients, from 60 to 70 per cent of the dry weight of the 

 organ, or 23 per cent of the moist weight, may be fatty acid. There is 

 no other organ in the animal body that is ever loaded with fat to this 

 extent. As in the depots, this liver fat might be derived either from fat 

 carried to the organ from elsewhere in the body, or it might represent 

 a surplus of manufactured fat. 



Transportation of Fat to the Liver. About forty hours after giving 

 phlorhizin to a dog, it has been found that enormous quantities of 

 fat appear in the liver; a few hours later, however, this excess of fat 

 may have entirely disappeared. Fatty infiltration of the liver is also 

 observed in phosphorus poisoning, although in this case the fat usu- 

 ally persists till the death of the animal. In man, in delayed chlo- 

 roform poisoning and in cyclical vomiting, considerable quantities of fat 

 may be present in the liver within a very short period of time after the 

 onset of the condition. There can therefore be no doubt that fat is 

 transported to the liver under abnormal conditions, but this can not 

 be taken as evidence that the liver has anything to do with fat metab- 

 olism in the normal animal. Such evidence has, however, been supplied 

 by Coope and Mottram, 51 who have shown, at least in rabbits, that a sim- 

 ilar invasion of the liver with fat occurs in late pregnancy and early 

 lactation. They also found that the fatty acid deposited in the liver 

 in late pregnancy gives an iodine value which lies nearer to that of the 

 mesenteric fatty acid than is the case in normal animals. Mottram con- 

 cludes that "wherever . . . there is abundant fat metabolism, the 

 liver is found to be infiltrated with fats, presumably to be handed on 

 elsewhere when worked up." It is interesting that the fetus is greedy 

 of unsaturated fatty acids. 



The most likely source of the fat transported to the liver is the fat pres- 

 ent in the depots, unless when digestion is in progress, when it may be 

 the fat from the intestine. That much of it comes from the depots is 

 easily demonstrated. Thus, the more extensive the infiltration of the 

 liver with fat, the more closely will this fat be found to agree with the 

 depot fat in its chemical characteristics. This has been very clearly 



