Osmic acid (2% aqueous sol.) . 4 parts. 



Clironiic acid (1% a(iueous sol.) . 1.") j);irts. 



Glacial acetic acid .... 1 part. 



The solution may lie kept on hand in a well-stopi)ered 

 bottle. Tissues must he in small ])ieces, one dimension of 

 whicli ought not to be more than one-twelfth or one-eighth 

 of an inch. The chromic acid might penetrate larger pieces, 

 the osmic might not. The tissues remain in the solution 

 about 24 hours, are then thoroughl}' washed in flowing 

 water, and tiie hardening com[)]eted in graded alcohol. 

 This solution is largely used in hardening tissues for cell 

 division, and foi- bringing out the finer details in the struc- 

 ture of the ])r()t()iilasni and nucleus. Unless the tissues 

 are well washed it is often hard to stain them. 

 Hermann's Solution. 



Hermann uses in place of the chromic acid in Flem- 

 ming's solution a 1% aqueous solution of platinum chloride, 

 the formula reading as follows: 



Platinum chloride (1% aqueous sol.) 15 parts. 



Osmic acid (2% aqueous sol.) . 2-4 parts. 



Glacial acetic acid .... 1 part. 



The pieces need to be small; they remain in the solu- 

 tion for 24 to 48 hours, are then washed in water, and 

 hardened in graded alcohol. Hermann's fluid is used with 

 good results in hardening for kar^^okinesis, spermatogenesis, 

 etc. 



Solution of Platinum Chloride, Osmic Acid, and Mercuric 

 Chloride. 



The author has found the following solution a verv 

 good fixative : 



Platinum chloride (2% aqueous sol.) 3 parts. 



Osmic acid (2% aqueous sol.) . 2 parts. 



Mercuric chloride (sat. aqueous sol.) 5 parts. 



It is especially useful for hardening the testes of mam- 

 malia. Ver\' small pieces are to be hardened for about 

 24 hours, are then thoroughly washed in flowing water for 

 12 hours, and the hardening completed in graded alcohol. 

 In testes hardened in this solution, the accessary nucleus is 

 very clearly seen in nearly every cell ; its change in shajoe 

 until it forms the "head cap" of the fully developed 

 spermatozoa can easily be traced. 



