SECT. 8] 



CARBOHYDRATE METABOLISM 



1033 



species, for with the sheep it appears early, at the end of the second 

 month of gestation, but does not rise much till the end of the fourth 

 month. With the pig it appears suddenly at the beginning of the last 

 fortnight of gestation. With the guinea-pig it appears at the 40th day 

 of gestation but does not rise very fast." Aron was not inclined to 

 accept the simple hypothesis of Claude Bernard that the glycogenic 

 function is taken on by the liver as soon as the cells are morphologically 

 ready to receive it. He regarded it as much more likely that the 

 passage of this function from placenta to liver was under the control 

 of an endocrine agency, and 

 was thus led to examine the 

 behaviour of the pancreas. 

 Laguesse had already pointed 

 out that the appearance of the 

 pancreatic islets in early em- 

 bryonic life was quite different 

 from that which they presented 

 later, and Aron extended his 

 work by showing histologically 

 that the second generation of 

 islets, i.e. the islets of Langer- 

 hans, appeared rather rapidly 

 out of the islets of Laguesse just 

 about the time when the glyco- 

 genic function was installing 

 itself in the liver. This relation- 

 ship held quite rigorously as 

 between the different animals ; thus in the sheep the islets of Langerhans 

 appeared first about the 50th day, while in the pig they did not appear 

 till the looth day. The significance of these findings can be seen from 

 Fig. 286. Aron also brought various lines of evidence together to show 

 that the Laguesse islets produce no insulin, as those of Langerhans do. 

 The transformation of the former into the latter may be very sudden. 

 "Cette veritable explosion endocrinienne ", said Aron, "pent se 

 declancher un peu plus tot ou un pen plus tard selon les cas. Quoi 

 qu'il en soit, on observe constamment une coincidence frappante entre 

 la presence de nombreux ilots de Langerhans dans le pancreas, et le 

 depot dans la foie d'une notable quantite de glycogene." Even in the 

 case of man, where Aron only worked out the appearance of the 



66-2 



Sheep 



Pi9 

 G.-pIg 



80 90 100 110 120 130 140 150 



10 20 30. 40 50 60 70 80 90 100 110 120 130 



J Days 



Fig. 286. 



