Cog HILL, SktJi of the Frog. 6i 



hour in the solution usually employed, and destaining with a 

 thirty per cent, solution of acetic acid. 



(c). Weigert's haematoxylin. The tissues were mor- 

 danted three hours in a one-half saturate solution of copper 

 acetate, stained three three to four hours in Weigert's haema- 

 toxylin, and differentiated in Weigert's decolorizer. Three 

 hours in the stain for Amphibian tissue has proved sufficient, 

 and no doubt less time would give good results. 



3. Methylene Blue. The solutions used in this method 

 were those employed by Prof. Huber, viz., one-tenth per cent, 

 solution of methylene blue in normal salt, fixed either in a sat- 

 urated solution of ammonium picrate or in a solution of ammo- 

 nium molybdate as follows : distilled water, 10 cc; ammonium 

 molybdate, i gram ; hydrochloric acid, i drop. For section- 

 ing, the latter was used; for examining m toto, the former. The 

 stain was injected beneath the skin of the head by means of a 

 hypodermic syringe. About six hours after the injection the 

 frog was killed and the skin removed. After exposure to the 

 air till the nerves were well differentiated, the tissues were 

 placed for one day in the fixatives mentioned. Those in am- 

 monium picrate were then changed to glycerine. Those in the 

 ammonium molybdate solution, were treated in the following 

 manner : one hour in 95 % alcohol, one hour in absolute alco- 

 hol, one hour in warm turpentine, and embedded in paraffin in 

 an oven at a temperature of 70° C. This method of dehydrat- 

 ing and embedding involves some decolorization. Neverthe- 

 less, it gives good results if the process be hastened as much as 

 is permissible. 



4. GoLGL Strong's modification of the silver method 

 was followed in the main. Small fragments of skin were placed 

 for 48 hours or more in a solution of 3^ ^ potassium bichro- 

 mate four volumes and i % osmic acid one volume. After four 

 days in a I ^ solution of nitrate of silver, they were washed 

 two hours in 95 ^ alcohol, one half hour in equal parts abso- 

 lute alcohol and ether, and one hour in warm turpentine. For 

 embedding, paraffin was used as with the methylene blue 

 method. 



