THE PANCREAS 45 



10 and 11), but if after such a period the animal is restored to 

 its normal state of nutrition, the usual proportion of islet tissue 

 is found. The most obvious explanation of this is that the 

 alveoli are reformed from the islet tissue. There is, however, 

 another possibility namely, that the islet tissue formed from 

 alveoli, as a result of changed physiological conditions, is not 

 reconverted into secreting tubules, but, having reached the 

 last stage of its career, degenerates and disappears. If this 



trans, c.. 



zym. 





trans, c. 



FIG. 11. Splenic end of the pancreas of a pigeon after a few days' inanition. 

 The increase in the amount of islet tissue is very marked (Vincent and 

 Thompson). C/. with Fig. 10. (Drawn by Mrs. F. D. Thompson.) 



Lettering same as for Fig. 9. 



be the case, we must assume that new alveoli are formed from 

 the existing tubules, and occupy the space recently occupied 

 by islets. On this hypothesis the more solid islets might be 

 regarded as nothing more than worn-out alveoli about to 

 disappear. Of the two possible views here put forward, the 

 present writer is inclined to support the former. 



Feeding dogs upon a purely carbohydrate diet also increases 

 the amount of islet tissue, and removal of the spleen from frogs 

 has a similar effect. 



