SECT. Il] 



FAT METABOLISM 



1 167 



important rise in the fat during the week before hatching — and it 

 will be remembered that analyses of other embryos than the chick 

 demonstrated fragments of the same set of curves. Facts of simple 

 observation, too, confirm the enhanced activity of fat metabolism 

 at the end of development. Metzner observed fat globules in the 

 liver of the chick on the 1 2th day, not before, after which time they 

 rapidly increased in number and in size, and this was but a con- 

 firmation of the earlier work of E. H. Weber. Nordmann, again 

 found no fat in explanted liver 

 cells from 8th or 9th day em- 

 bryos but an abundance in 

 those from the last week of in- 

 cubation. He noted that fat 

 added to the medium on which 

 the former were growing would 

 pass into the cells. Virchow, 

 studying the yolk-sac of the 

 chick histologically, observed 

 fat drops after the loth day, 

 but never before. On the quan- 



O Murray 



• Idzumi 



®Cahn (triglycer 



® Eaves 



® Liebermann 



Days 



Fig. 361. 



titative side, Riddle's estimations of fat in the yolk towards the end of 

 incubation, which will be mentioned again later, show a preferential 

 utilisation of fatty acids by the chick embryo. 



Important information on these questions has been gained by the 

 use of the dye Sudan III, which attaches itself to fat molecules and 

 indicates their presence. Sitovski was the first to make use of this 

 substance, and by feeding it to moths was able to obtain their eggs 

 deeply pigmented. Riddle then independently fed Sudan III to 

 laying hens (3 to 25 mgm. of the dye per hen per day), and observed 

 that the yolks of their eggs became red, or rather, that the yellow yolk 

 became red, the rings of white yolk and the latebra remaining pale 

 yellow, or becoming very pale pink, thus according with the chemical 

 analyses (see p. 286). Riddle succeeded in pigmenting the eggs of 

 turtles in the same way, and since that time his experiments on fowls 

 have been confirmed by many investigators (e.g. Hainan) . Gage & 

 Gage were the next to go into the matter, and, feeding hens on the 

 dye, incubated the resulting eggs. "As the yolk softens during the 

 process of incubation", they said, "the layered (pink and yellow) mass 

 becomes homogeneous and of a uniform pink. This is marked from 



