iigo FAT METABOLISM [pt. m 



the total amount of substance in the eggs. It will be admitted that 

 the whole subject of fat synthesis in these aquatic eggs urgently needs 

 re-examination. 



11-9. Fat Metabolism of Mammalian Embryos 



It has often been asked how fatty acids arise in the mammalian 

 embryo, since there is no yolk from which they can be transferred. 

 The obvious answer is that the foetal fat is suppHed through the 

 placenta, but this has to meet the objection that there is a good deal 

 of evidence against the existence of this transportation. It would per- 

 haps be more suitable to delay the consideration of this question till 

 the Section on the placental barrier, but it is too intimately associated 

 with fat metabolism. That the fat-content of the foetal blood is in- 

 dependent of the fat-content of the maternal blood was suggested by 

 the experiments of Oshima, who in 1907 studied the ultra-microscopic 

 particles of the foetal blood. Neumann had shown some years before 

 that the concentration of these in blood ran closely parallel to the fat- 

 content as determined chemically, and they are probably identical 

 with the "chylomicrons" of Gage & Fish. Oshima found that in the 

 guinea-pig the maternal blood has always a " massiger, " " zahlreich ", 

 or "massenhaft" number of fat-particles, but the early foetal blood 

 "sparlich". As the embryo developed, however, the number of fat- 

 particles in its blood rose greatly, and at birth nearly, if not quite, 

 equalled that in the maternal blood. It was significant that the con- 

 dition of the foetal blood seemed to be independent of the mother, for 

 fasting, Oshima found, would easily reduce the fat-particles in the 

 mother's blood to few or none, without having any effect on the 

 foetus, which was always as rich in fat-particles as it was scheduled 

 to be at the time of development in question. On the other hand, 

 if fat was fed to the mother in large amounts there^ was no effect on 

 the embryonic blood, although a large one on the maternal blood. 

 Oshima naturally concluded that fat was not transported from the 

 maternal to the foetal circulation. 



This received later a quantitative backing from various investi- 

 gators. Ahlfeld very early had reported large and inconstant dif- 

 ferences between maternal and foetal blood-fat in the dog, and had 

 shown that bacon feeding affected the maternal circulation only. 

 Kreidl & Donath in 1910 estimated the fat-content of guinea-pig 

 foetal blood in normal conditions (development time not stated) at 



