SECT. II] FAT METABOLISM 1193 



fatty acids except those of a certain degree of saturation, (2) that 

 the embryo can alter fats arriving at it by hydrogenation or de- 

 hydrogenation, or (3) that fatty acids do not pass the placenta at all, 

 and that the embryo forms its suppHes from carbohydrate, or possibly 

 from protein. In spite of the difficulties inherent in the third possi- 

 bility, it was the one which Wesson himself considered most likely. 

 For the further discussion of this problem, see the Section on placental 

 permeability. 



As regards the fat in the embryonic body of the mammal, Derman 

 has stated, as a result of the employment of histochemical methods, 

 more or less specific, that, up to the first month, the fat depots of 

 the human embryo contain mostly neutral fat and cholesterol esters, 

 less phosphatides and almost no free fatty acids, but, in the later 

 stages, neutral fat and cholesterol esters only. For other histochemical 

 work see Froboese and Berberich & Bar. Raudnitz found that the 

 melting-point of human fat was higher the younger the body, thus: 



but no explanation is available for this phenomenon. Another curious 

 observation, due to Dobatovkin, is that as growth proceeds the per- 

 centage of fatty acids liquid at room temperature increases. Thus, of 

 human fat from the shoulder region : 



The same fact, expressed more scientifically, is to be found in the 

 data of Egg and of Jaeckele & Knopfelmacher, the latter of whom 

 estimated the percentages of the three most important fatty acids as 

 follows : 



It is striking, from a comparative point of view, that the fat of the 

 egg-yolk of the chick should contain only 5 or 6 per cent, of oleic 

 acid. The data of Jaeckele & Knopfelmacher do not extend back 



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