1028 CARBOHYDRATE METABOLISM [pt. iii 



and a confirmation of some forgotten observations of Claude Bernard. 

 Another rather abrupt change in the Hver of the embryo chick was 

 revealed by the investigations of Heaton, who observed a change 

 in the biological properties of the liver cells on the 1 1 th day. Before 

 that time, its cells in tissue culture grow like epithelial cells (having 

 arisen, of course, as a diverticulum from the gut), but after that 

 time they grow like fibroblasts. Nor is this merely a morphological 

 difference, for after the 1 1 th day their growth is inhibited by yeast 

 extract, just as that of fibroblasts always is, but this is not the case 

 earlier. The change takes place regularly between the i ith and 12th 

 days, i.e. just about the time when the curve for glycogen in the 

 embryo shown in Fig. 280 inflects and rises sharply. In this con- 

 nection it is significant that Holton found that the liver will not grow 

 in chorio-allantoic grafts after the nth day. Nordmann has studied 

 the metabolic behaviour of explanted liver-cells. He states that 

 glycogen (observed histochemically) is synthesised by all stages from 

 the gth day onwards. The earliest ones (gth day) showed the presence 

 of glycogen very soon after explantation and retained it for nearly a 

 fortnight in culture, the later ones (i ith or 12th day) retained it only 

 for about 5 days. This synthesis of glycogen seemed to be independent 

 of the constitution of the medium. 



Serres' histological observations, illustrated in the Archives du 

 Museum d'Histoire Naturelle, have since been confirmed by J. T. Wilson 

 and by H. J. Allen. Allen, who seems to have been ignorant of the 

 pioneer work of Serres, made a histochemical study of the glycogen 

 in the yolk-sac of the chick at various stages. She found it to be 

 present from the earliest time onwards, distributed all over the 

 vascular area in the form of mahogany-coloured masses scattered 

 among the cells. The head ectoderm, the heart, and the myotomes 

 acquired glycogen very early also. "Apparently the yolk-sac", 

 said Allen, "furnishes a way-station in which carbohydrates are 

 stored as glycogen on their way from the yolk to the embryonic 

 tissue." 



Since the chick and the rabbit both exhibit the phenomenon of 

 the "foie transitoire", the practice may be very general. It has been 

 shown to take place in the ovo-viviparous selachian Mustelus vulgaris 

 by Blanchard, who reported that the vitelline membrane contained 

 abundant stores of glycogen. His methods were histochemical and 

 the research was never published in detail. 



