Herrick-Coghill, Nc7've Endings in the Skin. 53 



Note on the Methylene Blue Process. It appears that 

 we have had in one respect the usual experience with the meth- 

 ylene blue intj'a vitatn impregnation process. It is not difficult 

 to secure excellent impregnations of the nerves of the skin of 

 the Amphibia in which the nerve fibers are deeply and quite 

 selectively stained, yet it appears that there is a strong ten- 

 dency for the stain to be extracted or rendered diffuse by the 

 process of imbedding so that tissues which were very perfectly 

 stained in the glycerine are quite unsatisfactory in thin section. 

 It appears that the difficulty is in the action of the alcohol, which 

 is required in both the paraffin and the celloidin methods of im- 

 bedding. To obviate this difficulty we have resorted with good 

 results to the use of a mixture of gum arabic and glycerine. 

 The fragment is placed in glycerine or may be placed at once 

 in the gum-glycerine. After an impregnation of a day or two 

 in a closed bottle the specimen is mounted in a paper tray with 

 the mixture and the latter is allowed to evaporate till a consist- 

 ency is reached which will permit it being placed in the micro- 

 tome and sectioned. In this way sections are secured thin 

 enough to serve the pupose desired and these may be mounted 

 in gum-glycerine or may then be dissolved out of the gum and 

 treated in any way desired. 



