ISLANDS OF LANGEEHAKS 691 



Blood Supply. The blood supply of the islands differs sharply from 

 that of the acinus tissue, for, as soon as the artery enters, it breaks up into 

 a rich plexus of sinusoids, which permits the blood to come into very inti- 



Fig. 2. Duct with system of delicate tubules connecting with the islands stained 

 by injecting pyronin and neutral red into the blood vessels, after Bensley. 



mate contact with the cells. Special information regarding the lymphatics 

 is lacking. 



Innervation. Nerve fibers penetrate the islands in company with the 

 blood vessels, but their exact mode of termination has not yet been defin- 

 itely ascertained. We do not know whether they are secretory in nature. 



Embryology 



Origin and Development. According to Pearce, the islands of Langer- 

 hana first make their appearance in human embryos of fifty-four milli- 

 meters, in which they are formed as outgrowths of the primitive gland 

 tubules. At first they consist of solid clusters of a dozen or more cells 

 each ; they may be recognized by their pale staining nuclei and the affinity 

 of their cytoplasm for acid stains, like eosin. He describes the penetration 

 of blood vessels into these cell masses and their separation from the tubules 

 through connective tissue formation. It seems, however, from the recent 

 studies of Laguesse and Bensley, that the islands almost invariably re- 

 tain their connections with the ducts. The cells finally become roughly 

 arranged in columns and the island assumes its adult appearance. Slight 

 but significant variations in rapidity in development in different forms 

 are noted by Aron. 



In the newborn guinea pig Bensley has found that, in addition to the 

 well formed islands, there are myriads of single Langerhans cells incorpo- 

 rated in the epithelium of the acini. As development proceeds these iso- 



