On the Relations between the ,.Is]ets of Langerhans" etc. 95 



logists appear to favour the view that the islets of Langerhans con- 

 stitute a tissue sui generis, whose function is to control the metabolism 

 of sugar in the body. 



Diamare ^) has indeed put forward some experimental work in 

 support of this definite view as to the function of the islets. He finds 

 that the amylolytic ferment occurs only in the ordinary pancreatic 

 cells, while it is absent in the islets of Langerhans. He states that 

 the islet cells possess the power of inverting grape sugar. He is of 

 opinion that the islets are intimately concerned in the economy of 

 glucose in the body. The glycolytic action of the islets is in vitro 

 very weak and he looks upon the tissue as furnishing an endocrine 

 zymoplastic secretion. Hyperglycaemia and diabetes are in this view 

 the result of functional insufficiency of the islets. This observer further 

 records certain modifications occurring in the islets of Moietta tricirrata 

 as the result of the injection of glucose into the abdominal vein. 



Whatever may be subsequently discovered to be the true function 

 of the islets of Langerhans, their intimate anatomical relationship with 

 the zymogenous tubules, the numerous transition forms in all groups 

 of vertebrates, and the transformation of alveolus into islet, and vice 

 versa appear to us to prove conclusively that the islets are not organs 

 sili generis, but are an integral part of the ordinaiy pancreatic 

 tissue. 



As to whether the temporary modification into islet tissue corre- 

 sponds to a specialisation of function, the evidence is at present in- 

 conclusive. 



VII. Summary and Conclusions. 



1. In the vertebrate pancreas there appear to be two kinds of tissue 

 in addition to the ordinary zymogenous tubules, 1. the leptochrome tissue 

 forming the well known islets of Langerhans and 2. the hathychrome 

 tissue^), represented in mammals for the most part as small groups of 

 cells or even solitary elements scattered throughout the secreting alveoli. 



') Zentralbl. f. Physiol. Bd. XVIII. nr. 14. Okt. 1904; il)id. XIX oc. 4.. 

 20. Mai 1905; Internat. Monalsschr. f. Anat. u. Physiol. Bd. XXII. 1905, 

 -) See Appendix. 



