CHLORIDES ORGANIC ACIDS ETC. 61 . 



especially the " formative cells " of the parenchyma. This fixation 

 can be followed by staining with haemalum and orange G. 



Worms treated with Miiller's fluid for four days after twenty-four 

 hours' fixation in the Zenker-formic acid mixture give good results 

 with staining in acid fuchsin by the Kull method. Mitochondria are 

 preserved and stain. The addition of 4 parts of 2 per cent, osmic 

 acid to 12 parts of Zenker's stock plus 1 part of formic acid gives 

 preservation of neutral fat, together with the excellent general fixation, 

 and reduces the precipitation of mercuric chloride crystals in the fluid. 



The use of formic acid gives better results with the cold fluid than 

 are to be obtained with a hot acetic mixture. In comparison with a 

 Zenker-formalin fluid, such as Helly's, the results are superior. 



Dr. Guthrie has also used a strong Flemming's fluid with formic 

 acid (15 parts 1 per cent, chromic acid and 4 parts 2 per cent, osmic 

 acid with 1 part formic acid). Fixation for three days was followed 

 by twenty-four hours in pyroligneous acid and 1 per cent, chromic 

 acid (1 : 2), and twenty-four hours in 3 per cent, potassium bichromate. 

 This gives good histological features and preserves both neutral fat and 

 mitochondria. It can be followed, with splendid results, by staining 

 in crystal violet according to Benda's alizarin method. The crystal 

 violet is a 3 per cent, solution in 95 per cent, alcohol in an equal volume 

 of anilin water 



