19 



was gently warmed, pour-ed over- the slide for ten seconds, and 

 then washed away quite thoroughly with distilled water. Stain- 

 ing was done with either the pure stain of Nissl, or with the 

 same diluted with an equal volunie of ^^ acetone; the results 

 did not seem to differ very much. In either case, the stain 

 was heated and allowed to act for five minutes. Differentia- 

 tion with 0.1* aluo-i solution for Just a few seconds, until the 

 sections appeared distinctly red, was followed by a brief rins- 

 ing witl' water. The results given by this process have been of 

 value as an accessory to the pure methylen-blue stain, but they 

 are far from supplanting the original method. 



b. Intra-Vi tuT Injeoticn. — The coloration of the nerve- 

 cells through intra-vitua. injection of methylen-blue was given 

 a most thorough trial, a large nuirber of animals being utili- 

 zed for this purpose. The subcutaneous injection preferred by 

 Meyer ('96) is not practicable for Mustelus because of the 

 absence of either loose areolar tissue or of lymph spaces. 

 The syringe was therefore inserted directly into the vascular 

 system. A nf solution of methylen-blue, FX brand, was injected 

 some four times during the course of an hour. Beginning with 

 a small quantity, the amount rose successively until as much 

 as 30 c.c. was introduced in the final injection, making some 

 50 c.c. in all. This whole process was governed, however, 

 not by fixed quantities of the reagent nor by exact periods of 

 time, but by the stopping of tlie heart's action and the blue- 



