ORGANIC ACIDS. 23 



of acetic acid on the slide. With the neutraliza- 

 tion of the alkali they often become somewhat 

 opaque, but may be re-cleared, often to great trans- 

 parency, by laying them in glycerine. 



In the study of crystals, those composed of an 

 oxalate may be distinguished by being insoluble in 

 acetic acid, but soluble in hydrochloric acid, 

 (p. 22} ; while salts of carbonic acid, occuring as 

 crystals or as incrusting components of the cell- 

 wall, are soluble with effervescence in either. 



Acetic acid sharply differentiates the nucleus, 

 and is often a valuable medium in the study of 

 the intimate structure of protoplasm. Stras- 

 burger 1 employs a one per cent, aqueous solution 

 for fixing the nucleus when staining the latter 

 with methyl-green ; at the same time it often 

 clears up protoplasmic structures, and swells the 

 condensed ectoplasm. 



Acetic acid has also found application in coch- 

 ineal solution, and in glycerine in which prep- 

 arations stained with carmine are to be preserved. 



OXALIC ACID. 



The aqueous solution 2 is employed with certain 

 coloring matters in staining tissues. The alcoholic 



1 Zellbild.u. Zelltheil., 1880, 3 ed. 



2 Dippel: Das Mikroskop, I., p. 285. Frey: Das Mikroskop, p. 77. 

 Bachmann: Dauerpraparate, p. 27. Wiesner: Technische Mikroskopie, 

 pp. 247, 258. 



