136 



or even thicker. Fasten the sections to the slide or carr}^ them 

 through in watch-glasses. Stain the sections in a .5% aqueous solu- 

 tion of methylene blue for 5-10 minutes, heating it until it steams ; 

 rinse in water and deh3'drate, clear in oil of origanum or cajuput, 

 and mount in balsam. The nerve cells and nuclei will be stained 

 blue, all else colorless. In the cell bodies the corpuscles of Nissl 

 will be stained. Should the stain be not selective enough, differen- 

 tiate for a few seconds before dehydrating with a mixture of aniline 

 oil, I part, 95% alcohol, 9 parts. 



§ 145. General methods, vom Rath's and Zenker's fluids 

 are recommended for the fixation of nervous tissue ; either paraffin 

 or collodion may be used in imbedding ; Delafield's hematoxylin 

 with picrofuchsin (strong formula, b) as counter-stain is recom- 

 mended for staining, though other hematoxylins may be used as well. 



SILVER NITRATE IMPREGNATIONS. 



§ 146. The preparations stained bj' means of nitrate of silver 

 were prepared as follows : The fresh tissue was washed well for a 

 minute or so in distilled water to remove from the surface all album- 

 inous substance, and then transferred for 2-5 minutes or longer to a 

 yi% aqueous solution of silver nitrate ; it was again rinsed in water 

 and in it exposed to direct sunlight until a light brown. When, by 

 examination with the microscope, the stain was found to be suf- 

 ficient it was again rinsed in water and placed in glycerin or alco- 

 hol. Employed in this manner with fresh tissue, silver nitrate 

 stains the cell cement, affording thus negative images of the cells. 



§ 147. Silvering Vascular Epithelium. In order that the 

 vasular epithelium of small arteries, veins, and capillaries should be 

 well demonstrated, silver nitrate solutions of ^ to ^2% strength 

 must be injected into the vessels. 



§ 148. Procedure. Connect a canula with the artery supply- 

 ing the alimentary canal (superior mesenteric) or the brain (carotid) 

 and inject distilled water until the water flows out of the returning 

 vein colorless. Then immediately inject the silver solution until it 

 runs from the vein. After a minute or two follow with distilled 

 water. Place the intestines and mesentery in water and expose 

 them to the light until they become slightly browned. Strips of the 

 muscular coat of the intestines, especially of the rabbit, will show 



