342 R. R. BENSLEY 



Dale ('05), Vincent and Thompson ('07), Mankowski ('01), 

 Tschassonikow ('00), Dewitt ('06) and others. But with the 

 exception of Laguesse, Weichselbaum and Kyrle, and Helly, I 

 have found no authors who have seen direct connections with 

 the ducts, though Lewaschew ('86) in his injections from the pan- 

 creatic duct succeeded in forcing the mass into islets. 



By means of new methods for vital staining of islets and ducts 

 I have been able to show that the relations of islet to duct in the 

 guinea pig are precisely as described by Laguesse, and that while 

 there is a certain number of detached islets, the rule is epithelial 

 continuity between islet and duct or between islet and acini or 

 both. This has been accomplished by means of the combined 

 staining of the pancreas with pyronin and neutral red, or pyronin 

 and janus green, or methylene blue and neutral red. The methods 

 for using these stains are described under technique, and it is 

 necessary here merely to state that as far as the epithelial ele- 

 ments of the guinea pig of the pancreas are concerned, pyronin 

 or methylene blue intra vitam stain only the duct cells, leaving 

 the others colorless. The stain is a diffuse one in the epithelial 

 cells, and strangely enough the nuclei stain, though the nuclei 

 of other cells in the pancreas remain unstained. The intensity 

 of the stain is greatest in the smallest ducts and diminishes in 

 intensity as the size of the duct increases. The centroacinous 

 cells, as might be expected, stain intensely. By using two dyes 

 together, a double stain may be obtained, enabling one to delimit 

 exactly the two tissues, islet and duct. The pyronin prepara- 

 tions must be studied fresh, but as the dye reduces slowly in the 

 tissue, the preparation may be kept for several hours. Treat- 

 ment of the preparation with ammonium molybdate makes the 

 dye somewhat more resistant to glycerine, but does not protect 

 it from alcohol. Glycerine mounts last for several days but grad- 

 ually diminish in value. The methylene blue preparations, on 

 the contrary, may be made permanent in the usual way by am- 

 monium molybdate, this method also permitting imbedding in 

 paraffin, and sectioning. Total mounts are, however, most val- 

 uable because they enable one to dispense with reconstruction 

 and to see the whole plan in a single specimen. 



