192 



FAT METABOLISM [pt. iii 



colourless. Similar experiments were carried out by Mendel & Daniels 

 in 191 2, using Sudan III and Biebrich scarlet, and working on preg- 

 nant rats and cats, but always the embryos remained absolutely 

 colourless, although the maternal fat was brightly coloured. Baumann 

 & Holly later still obtained the same quite negative results. There is 

 some likelihood that the placenta could detach the dye from the 

 fatty acids. 



Then Hofbauer in 1905 fed cocoa butter to dogs, and claimed to 

 have identified lauric acid in the foetal fat after some days, but its 

 presence was not really estabhshed, and the experiments might well 

 be repeated. Thiemich's work was better, although it antedated that of 

 Hofbauer by some years. Thiemich fed certain dogs on cocoa butter 

 and others on linseed oil cake, with the following results: 



Iodine value Iodine 



of fat value of 



in food foetal fat 



Cocoa butter 8 7i"3-73'i 



Linseed oil 120 ^dS-Jo-^ 



from which he naturally concluded that the foetal fat maintained 

 its accustomed iodine number quite unchanged, no matter what was 

 the degree of unsaturation of the fatty acids entering the maternal 

 body. Thiemich did not estimate the iodine value of the maternal 

 fat, but assumed that it would vary closely with the food fed. In a 

 later paper, however, he modified his conclusions somewhat, because 

 he estimated simultaneously the iodine value of the maternal fat, and 

 found that it did not change as much as he had expected, e.g. only 

 from 30 to 50. Becker afterwards discussed the question further 

 without adding anything to it. Wesson in 1926 using the method of 

 bromine addition compounds, fed cod-liver oil to one set of pregnant 

 rats, and ordinary butter to another set, and found, although the 

 bromine number of the fed fats was extremely different, hardly any 

 difference was to be seen in the foetal fat. 



Cod-liver oil (bromine number 0-210) 

 Butter (bromine number 0-0031) 



This is probably the most reliable, as it is the most recent, work on 

 this subject. Wesson suggested a choice between three possible ex- 

 planations: (i) that the placenta has a selective action, rejecting all 



