702 METABOLISM 



way house in the preparation of the fatty-acid molecule \'ov consumption 

 in the tissues. Fat is a material containing large quantities of poten- 

 tial energy. While in the depots this potential energy is so locked away 

 as to be unavailable for tissue use. To make it available the depot fat 

 is carried to the liver, where the energy becomes unlocked but not actu- 

 ally liberated. The fat is then transported to the tissues, and the libera- 

 tion of the energy occurs. Neutral fat is like wet gunpowder: it con- 

 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, hut 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. 



That transportation of fat to the liver occurs is very readily demon- 

 strable both in the laboratory and in the clinic. About forty hours 

 after giving phlorhizin to a dog, it has been found that enormous quan- 

 tities 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 ;il so observed in phosphorus poisoning, although in this case the fat 

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

 roform poisoning and in cyclical vomiting, enormous 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 been supplied by Coope 

 and Mottram, 51 who have been able to show that, at least in rabbits, a 

 similar 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 



