12 John Rennie, On the Relation of the Islets of Langerhans etc. 



rapidly that tlie change "can scarcely be interpreted as a morphological 

 one". It is a morphological fact whose importance depends entirely upon 

 whether the change indicates normal functional change or whether it is a 

 degenerative one. The former is assumed by the observers and the 

 structural changes in the size of the cell and of the nucleus are thereby 

 accounted for. This implies in particular very rapid reorganisation of the 

 nuclear mechanism with resulting change of function; the change in fact 

 taking place in the course of a few hours. Such an occurrence we have 

 difficulty in realizing and the authors themselves are evidently in the 

 end not satisfied, for on page 95 they state. "As to whether the 

 temporary modification into islet tissue corresponds to a specialisation 

 of function, the evidence is at present inconclusive." One other re- 

 markable fact upon which Vincent and Thompson are silent is that of 

 the blood supply of the pancreatic islets. Observers are agreed that 

 in normal islets there is a rich and distinctive capillary supply. Can 

 it be shown that these transformations into islet tissue of secreting 

 alveoli in fasting, in hibernation, and under the influence of secretin 

 involve a reorganisation of the capillary system in the region of the 

 transformed cells? Such would be welcome and convincing evidence 

 that transformations are of normal occurrence and that the transformed 

 islets of experiments are functionally similar to those occurring natu- 

 rally. But we find no reference to such a morphological agreement 

 and if it occurs, it ought certainly to be emphasised. 



In conclusion it may be observed that all modern investigators are 

 at one that these islets are neither effete nor otherwise useless structures, 

 but ascribe to them an internal secretion. Whether they are normally 

 dependent upon the zymogenous tissue for their existence (which seems 

 unlikely) or not, they are always present, and there seems to be little 

 doubt that they fulfil an important role in vertebrate metabolism. 

 That their function is the control of the amount of sugar in the blood 

 has been the one most frequently suggested, and some experimental 

 work has been put forward in support of this (Rennie & Fraser, Bio- 

 chemical Journal, II 1906, pp. 7 — 19), but it cannot as yet be said to 

 have been satisfactorily established. 



