240 bulletin: museum of compakative ZOOLOGY. 



entirely. Iodine-alcohol was used as a test for the presence of the sub- 

 limate, being renewed until it no longer lost color. Tissues treated by 

 Prentiss's method ai'e usually passed through weaker and weaker grades 

 of alcohol to water and then placed in a solution of ammonia (one part 

 ammonia to four parts water) for twenty-four hours, in order to remove 

 any Nissl substance from the sensory cells ; but I have not found it 

 necessai-y to do this in the present case. When the sections were ready 

 for staining, the slides were placed for fifteen minutes or more in an 

 aqueous solution of ammonium molybdate (1:4000), which was kept at 

 a temperature of 35°-40°G y ., preferably on a water-bath. The slides 

 were then rinsed well in distilled water, finally flooded with it and placed 

 for about a minute in an oven at a temperature of 58° C. They were 

 rinsed quickly and stained for not more than five minutes in an aqueous 

 solution of toluidin blue (1 :3000) at a temperature of 58° G. The 

 excess of stain was rinsed off with distilled water and the slides were 

 passed successively to 96 per cent alcohol, to 100 per cent, and to xylol. 

 The sections should be thoroughly dehydrated and then freed from alco- 

 hol, otherwise they are likely to deteriorate rapidly. If the fibrils are 

 not differentiated the sections should be passed through the alcohol more 

 slowly. 



Even when the fibrils are properly differentiated, it is often difficult to 

 make out precisely the extent of the sensory cells and to distinguish 

 edges or wrinkles on the surface from neurofibrils. It was therefore in- 

 structive to counterstain the sections in a weak alcoholic solution of 

 brange-G. 



The fluids devised by vom Rath ('95) are well known. The mixture 

 which I used is described by him on page 282. The tissues were fixed 

 for three or four days in the fluid and then, after being rinsed quickly 

 in methyl alcohol, were placed in crude pyroligneous acid for sevei'al 

 days. Dehydrating in the different grades of alcohol was done in the or- 

 dinary way, except that the tissues were left in 90 per cent alcohol for 

 several days or until the alcohol was no longer colored. Sections were 

 then made in the ordinary way. Such preparations vary greatly in 

 value. The impregnation with osmium is most complete near the sur- 

 face ; hence the pieces should be made as small as possible. The fluid 

 differentiates the linin substance of the nucleus, but the nuclear fluid is 

 not stained at all. The general fixation seems to be much superior to 

 that obtained by corrosive sublimate or ammonium molybdate. The 

 vom Rath fluid has both the advantage and the disadvantage that it im- 

 pregnates all of the fibrils in the cell. While, therefore, it reveals the 



