126 



alcohol, changing once or twice if the alcohol becomes 

 discolored. It is not necessary to remove all the picric acid 

 before proceeding to the further preparation of the speci- 

 mens. 



Picro-sulphuric acid. Distilled water 100 parts, sulphuric 

 acid 2 parts, picric acid as much as will dissolve. Treat 

 specimens as for picro-aceto-sublimate. 



Mercuro-nitric mixture. Distilled water, 400 c.c. ; alcohol, 

 60$ strength, 50 c.c. ; nitric acid, 46$ strength, 7 c.c. ; glacial 

 acetic acid, 2 c.c. ; corrosive sublimate, 9 grams. Leave speci- 

 mens in this mixture for from three to twelve hours ; twenty- 

 four may be better in some cases. Wash in 70$ alcohol and 

 remove to fresh 70$ alcohol, to which a small amount of 

 tincture of iodine has been added to hasten the removal of 

 the corrosive sublimate ; leave in this solution for two or 

 three days and then transfer to 85$ alcohol for indefinite 

 keeping. 



CJiroino-nitric acid. Alcohol, 70$ strength, 3 parts ; nitric 

 acid, iof strength, 4 parts ; chromic acid y 2 % strength, 3 

 parts. Leave specimens in this mixture four to eight 

 hours, and wash in 70^ alcohol. Leave in 70$ alcohol for 

 twenty-four hours, and remove to 85^ alcohol for keep- 

 ing. 



Penetration can be more certainly effected if the fixing 

 fluid is used warm. Where the killing is done in the labo- 

 ratory and the fluid can be readily slightly heated, it is well 

 always to do it. 



In addition to the fixing agents of which formulae have 

 been given, other fixing agents, a host of which are described 

 in chapters IV. and V. of Lee's Vade-Mecum, may be used. 

 For cytological work, the osmic acid agents, such as Flem- 

 niiug's chromo-aceto-osmic acid (Lee's Vade-Mecum, p. 40), and 

 Hermann's platino-aceto-osmic acid (Lee's Vade-Mecum, p. 45), 

 should be used. 



