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On Bleaching and Washing Microscopical Sections. 



By Sylvester Marsh, Jun., L.R.C.P., &c., &c. 



Communicated by A. de Souza Guimaraens, F.R.M.S. 



{Read February 21th, 1880.) 



Now that the practice of staining vegetable tissues, and especially 

 vegetable sections, is so universally adopted, it has become of moment 

 to determine by what means the previous decolourization of such 

 objects may best be effected. That by some process or other a pre- 

 liminary bleaching ought to be carried out previous to the applica- 

 tion of staining agents will be admitted by all, but the precise 

 process to follow so as to obtain the best results with the greatest 

 quickness and safety does not seem so clear. The agents most 

 commonly used for bleaching are : — (1) Alcohol ; (2) Solution of 

 Chloride of Lime; (3) Labarraque's Solution of Chlorinated Soda, 

 made by decomposing Lime Chloride by the action of Sodium 

 Carbonate. Now to each of these methods there are serious objec- 

 tions. Alcohol is very slow in action and not always certain in 

 result. Solutions of Lime Chloride and Chlorinated Soda do 

 bleach, it is true, but they also disintegrate and destroy ; so that 

 many delicate tissues when subjected to the action of either of 

 these solutions become utterly ruined. The former solution, in 

 addition to its direct destructive influence, has a great tendency to 

 })ermit of the formation on its surface of a scum of Carbonate of 

 Lime ; this, sinking into the fluid, settles itself upon the sections, 

 so that if they escape absolute destruction they are in danger of 

 becoming coated with a brittle film, which proves equally ruinous to 

 them. The inconveniences here mentioned led the writer to discard 

 tliese methods of bleaching and to resort for this purpose to the 

 direct action oi free chlorine. As this process proved itself capable 

 of being so easily carried out, and yielded such safe and satisfactory 

 results both to himself and to several working microscopists to 

 ■whom he communicated the method, he has thought that a brief 

 description of the process might not be unacceptable to microsco- 



