The Mickoscope. 245 



luted with 5-6 vols, of 70 per cent, alcohol, and if a precipitate 

 forms either at the time of dilution or later add two or three 

 drops of hydrochloric acid and shake well. With it very beau- 

 tiful preparations of ciliated epithelum can be made in the fol- 

 lowing manner. A fresh trachea is opened and the above fluid 

 slowly flowed over the inner surface, and then followed by TO 

 per cent, alcohol, to which has been added \ oz. of oxalic acid, 

 until the red brown color has changed to a yellow brown. The 

 epithelium is then scraped off and mounted in glycerine. Deli- 

 cate protoplasmic processes are also well preserved in the same 

 way. If sections cut in a freezing microtome, or thin sections 

 cut after the usual methods, be first treated with the iron and 

 then with a weak solution of gallic acid an exquisitely shaded 

 and durable iron stain in gray and black results. All objects 

 treated with the iron must be very small as its action is limited 

 to the surface. 



Osinic acid is best followed by a very weak solution of am- 

 monium carbonate, acetate of potash or picrocarmine. These, 

 especially the two former, neutralize and remove all traces of 

 the acid, and so prevent blackening. Nitric acid specimens 

 may be treated with a 1 or 2 % solution of alum. Water should 

 not be used after picric acid, only alcohol, and to facilitate the 

 extraction of the acid and color, the bath may be placed in a 

 warm chamber, (50° -60° C). 



HARDENING. 



Alcohol, in various per centages of strength, is now the only 

 fluid used to give to structures the necessary consistency for sec- 

 tion cutting. It may be used after any killing fluid, a low grade 

 first, and then successively higher ones. Specimens should, just 

 before staining or embedding, be placed for one or two hours in 

 96 or 98 % alcohol, which I find answers as well as the more ex- 

 pensive absolute. The hardening of specimens should always 

 be conducted at a low temperature, in summer in a cool cellar or 

 refrigerator and in winter in a cool room. In any case, however, 

 weaker alcohol than 70% should not be used more than 2 or 3 

 hours at a time, as maceration will almost certainly occur. To 

 preserve specimens for future use, I find 85% alcohol to serve 

 the purpose well. 



