500 MANUAL OF HISTOLOGY. 



The numerous lymphatics require closer attention than has, up to the 

 present, been bestowed upon them. 



The gland vesicles of the pancreas are clothed with cubical cells. In 

 the full-grown rabbit these present in their inner half, or that next the 

 lumen of the gland, fatty particles, while the middle portion in which the 

 nucleus lies, and external to the latter, is clear. 



The excretory canals possess rather thin walls without muscular ele- 

 ments, in which are embedded, at the lower portion, a number of small 

 racemose mucous glands seated in the mucosa. 



If we examine closely in animals the clothing of columnar cells, we 

 find that from the beginning they are not particularly high. But in the 

 branches they decrease more and more in length, until, finally, in the 

 gland vesicles we meet with flattened epithelium, reminding us, in many 

 respects, of vascular endothelium. These are the centro-acinal cells of 

 which we have already spoken in considering the salivary glands ( 245). 

 They were first seen here by Langerhans. 



By careful injection of the excretory canal- work, the same system 

 of extremely fine secreting tubules may be brought to view in the 

 pancreas (fig. 297), as that to which we have already so frequently alluded 

 (Langerhans, Saviotti). 



As regards the nerves nothing certain is known. According to Pfliiger 

 their mode of termination is the same as in the salivary glands. 



The development of the 

 pancreas takes place very 

 early from the posterior 

 wall of the duodenum in 

 the form of a small sac- 

 cule or bud. 



As far as the composi- 

 tion of the alkaline react- 

 ing tissue of the gland 

 is concerned, nothing is 

 known. Its sp. gr. is, 

 according to Krauxe and 

 Fischer, 1 '047. A series 

 of very interesting decom- 

 position products, how- 

 ever, have been met with 

 in the fluid saturating the 

 gland ; in the first place 

 leucin in large quanti- 

 ties, and a considerable 

 amount, comparatively, of 

 tyrosin ( Virchow, Stae- 

 delcr, and Frerichs) : fur- 



Fig. 49.-Va 8 cular network of the pancreas from the rabbit. 



(Scherer), sarkin or hypoxanthin (Gorup), lactic acid, (and in the ox) 

 inosite (Buedelcer and Cooper Lane). Among these leucin (and tyrosin?) 

 have been remarked in the secretion of the gland, with which they find 

 their way into the intestinal canal. 



In a state of rest, or, more properly speaking, of slow secretion, the' 

 gland in question appears pale. When, on the other hand, it is actively 

 functionating, from about the fifth to the ninth hour after the reception of 



