200 John Rennie, 



commencement of observations. There are admitted individual diffe- 

 rences in respect to the amount of islet tissue present, and if it be 

 the case (as held by Dale, and Vincent and Thompson) that this amount 

 is, to express it mathematically, a function of the physiological condition 

 of this individual, then the difficulty of estimating it at the commence- 

 ment of an experiment is considerable. Dale recognises that the effects 

 produced must be such that they extend beyond the known limits of 

 variation under normal conditions. This means that abnormal conditions 

 are required to prove his case. Consequently when he interprets a 

 transformation as possibly a "reversion to an embryonic type" he is 

 probably quite right. It seems abundantly clear from the experiments 

 of Vincent and Thompson that in the experiments with secretin rapid 

 changes do occur, and it is possible that prolonged fasting may indeed 

 produce degenerative changes in which the alveoli revert to embryonic 

 conditions, and that it is possible to detect transition stages of this 

 degeneration. It is of course rather unlikely that these supposed de- 

 generate patches should be absolutely indistinguishable from true islets, 

 and this Vincent and Thompson assert to be the case with regard to 

 the transformed tissue observed by them. We must not however lose 

 sight of the fact that the conditions are abnormal, and that the results 

 afford no proof that such transformations take place under normal 

 conditions in nature. Consequently, so far as the experiments with 

 secretin are concerned we do not think they prove a function in ex- 

 haustion for the islets. Vincent and Thompson indeed state that in 

 their experiments with mammals injection of secretin was followed by 

 "a decided increase in the amount of islet tissue" and that this change 

 "which can occur within a few hours can scarcely be interpreted as 

 a morphological one, but must, on the other hand, be considered as 

 representing a phase of physiological activity". This argument is very 

 plausible; it is certainly not conclusive, for the morphological aspect 

 cannot be put aside in this way and the force of it is further greatly 

 weakened by Dale's statement that "exhaustion of the mammalian 

 gland (with secretin) was not found possible unless the animal was 

 also bled". Regarding the results obtained in fasting experiments it 

 is not beyond possibility that the changes observed are degenerative, 



