SECT. II] FAT METABOLISM 1195 



rapidly, and after 80 hours of post-natal life has reached a level very 

 like that of the maternal liver. As the figure shows, the fatty acid 

 concentration in the maternal liver is unaffected by gestation. "The 

 livers obtained from young embryos", said Imrie & Graham, "re- 

 sembled histologically and chemically adult hepatic tissue, whereas 

 in embryos fully developed the liver was yellow in colour and 

 showed chemically a large accumulation of fat. ... A fatty infiltra- 

 tion of a physiological kind occurs in the livers of embryonic 

 guinea-pigs." The synchronous behaviour of the iodine value was 

 very interesting, for, as Fig. 370 shows, it remained throughout the 

 process in the neighbourhood of no, i.e. much above the iodine value 

 of the embryonic connective tissue fat, which had an iodine value of 

 about 85. The rises and falls on the curve are probably not significant, 

 but the fat of the embryonic liver seems always to be a little less 

 unsaturated than that of the maternal liver. The fact, however, that 

 its iodine value was no precluded all possibility of the infiltration 

 being one of tissue fat, as in the adult. It seems likely also that there 

 is a slight decline in the iodine value of the embryonic liver fat; 

 for embryos under 40 gm. it could be said to be generally iii, and 

 above 40 gm. nearer 103 or 104. The difference between the average 

 maximum and minimum fat values of the embryonic liver is 9-94 per 

 cent. If we assume that this was fat coming from the connective 

 tissue and having an iodine value of 85, and added to the 3-16 per 

 cent, having an iodine value of 109, the resulting iodine value should 

 be 91, but instead it is at its lowest 103. It would be very interesting 

 to have a parallel set of data for the liver of the embryonic chick, 

 for, as we have already seen, there are ocular evidences for a fatty 

 infiltration there also. 



It is generally admitted that the liver desaturates fatty acids brought 

 to it, and that when it is infiltrated with connective tissue fat it falls 

 behind in this work, with the result that the low iodine value is found. 

 One must therefore conclude either that the liver of the embryonic 

 guinea-pig can desaturate relatively much larger amounts of im- 

 ported fat than is the case in extra-uterine life, or that the fat taken 

 up by the embryonic liver is fat which has already been desaturated 

 by the maternal liver or by some other tissue. As desaturation is the 

 preliminary to combustion, Imrie & Graham's results raise the 

 suspicion that fatty acids may play a more important part in the 

 provision of energy for the mammalian embryo than has been sup- 



