164 PEABODY. [VOL. I. 



posed of thick celloidin colored with Prussian blue was used 

 until it appeared at all the pores belonging to this system. 

 The specimen was then put into 20/0 nitric acid and left for 

 one to three days, until the skin and tissues were softened 

 enough to be easily removed with needle and fqrceps. A 

 careful dissection left a deep blue cast of the canals with their 

 finest ramifying tubules. Maceration is stopped and the 

 preparation kept indefinitely in a 2^0 formalin solution. The 

 course of the ampullary canals was readily followed by probing 

 with black bristles. 



Since 2ofi nitric acid softens bone, muscle, and connective 

 tissue, at the same time hardening more or less the nerve tis- 

 sue, specimens which have been thus macerated for a day or 

 two furnish favorable material for tracing nerve trunks and 

 fibers to their finest ramifications. 



For general histology Hermann's fluid and corrosive sub- 

 limate have proved the best fixing agents. Iron haematoxylin, 

 with orange G as a counter stain, has given very satisfactory 

 histological results. 



Method employed in using Methylcne Blue. - - After con- 

 siderable experimentation I have come to adopt the following 

 as a method of procedure for the successful application of 

 methylene blue to selachian material. The head of a live 

 dogfish is severed from the trunk, the snout cut open, and 

 a solution of methylene blue injected with a hypodermic 

 syringe into the gelatinous tissue in which the ampullae are 

 imbedded. I have obtained equally good results with i^fo, 

 I f > I 1 ?/ ' sV/k solution f the blue, but have found the 

 JQ^> the most convenient. After the stain has been allowed 

 to act for an hour and a half, a small clump of the ampullae is 

 removed to a slide and teased out so that each ampulla is iso- 

 lated and thus exposed to the air. The slide is then examined 

 under a low power. 



One of the most important factors in securing a successful 

 stain is that of exposure of the tissue in the air. I have often 

 found on looking over an apparently worthless series of ampul- 

 lae a second time that the fibers have become well stained, this 

 result being due apparently to the few moments of further 



