SECT. II] FAT METABOLISM 1179 



The determination of the non-volatile fatty acids showed them to 

 amount to precisely 50 per cent, of the total extract in each case, 

 so that the increase in them corresponded with the increase in the 

 total extracts. McClendon explained the slight lowness of Gortner's 

 figures as compared with his own by referring to the extreme diffi- 

 culty of removing by extraction the last traces of phosphatides from 

 yolk, owing to their association with vitellin. McClendon found the 

 MoHsch reaction negative on the whole egg, and could obser\'e no 

 reduction of copper after total hydrolysis (experimental details not 

 given), so he concluded that no carbohydrate groups were present, 

 and that the increase in fatty acids must be due to the destruction of 

 protein molecules. The evidence for this view was insufficient. 



Some histochemical investigations have been made on the develop- 

 ing amphibian egg. The work of Konopacka and of Konopacki & 

 Konopacka is especially detailed, and Hibbard has given an ex- 

 haustive study of the histochemistry of the development of the 

 anuran, Discoglossus pictus. Unfortunately, as I have pointed out 

 before, we have no guarantee that the substances which the histo- 

 chemical worker studies are the same as those which we analyse and 

 measure by purely chemical methods, though they may be, and 

 usually are, called by the same names. For this reason it is very 

 difficult to know what emphasis to lay on the findings of these workers. 

 Thus Konopacki & Konopacka, who worked with the embryos of 

 Rana temporaria, reported a disappearance of "fat" during the segmen- 

 tation stages, and concluded that "the intensity of metabolism is 

 parallel to the morphogenetic changes", though how this result could 

 be arrived at from the study of stained sections is not clear. But Kono- 

 packi & Konopacka had less to say about neutral fats than about 

 lipoids, as the Flemming-Ciaccio method is supposed only to reveal 

 the presence of the latter. However, "in the early stages of develop- 

 ment ", says Konopacka, " the fatty acids are utilised, for the number of 

 droplets staining with osmic acid are more numerous and larger than 

 those which stain with Sudan III after fixation according to Ciaccio's 

 technique. In later (post-gastrula) stages, however, the two kinds 

 of droplets are of the same size, and eventually the ' lipoid ' droplets 

 disappear completely, once the structure of an organ is determined". 

 Hibbard says that, during the early development of Discoglossus, 

 there is little change in the distribution or appearance of the fat 

 globules, but just before hatching they begin to increase in number 



