2O MICRO-CHEMICAL REAGENTS. 



of protoplasm. As its vapor attacks the mucous 

 membrane of the eyes and air passages, the use of 

 the osmiamid has been recommended, instead of 

 the acid, which it replaces well in all reactions. 

 Oil and fats reduce osmic acid, precipitating me- 

 tallic osmium, which colors the oil drops brown or 

 even black. Tannin is recognizable by the same 

 reaction. 



A one per cent, solution is especially valuable for 

 the instantaneous hardening of living protoplasm. 

 The stages in the division of the nucleus of cells, 

 and other structural peculiarities of protoplasmic 

 bodies are thus fixed in a few minutes, and, after 

 washing, may be preserved for future study in a 

 dilute solution of glycerine, which, however, has 

 the disadvantage of rendering the preparations 

 very transparent. 



Recently perosmic acid has been used in the 

 study of young meristem tissues. 1 The organs to 

 be studied were laid in a very dilute aqueous solu- 

 tion (.1-1 per cent.) of the acid until they black- 

 ened, after which they were treated with alcohol, 

 cleared with clove oil, and imbedded for sectioning 

 in cocoa-butter (butyrum cacao of pharmacists). 

 The sections were mounted in Canada balsam. 



A mixture of nine parts of .25 per cent, chro- 

 mic acid and one part i per cent, perosmic acid 



1 Parker: Journ. Roy. Microsc. Soc., 1879, ^v P- 3% 2 ' I have not 

 tested the method. 



