METHODS OF HARDENING AND PRESERVING. 379 



for the 'prevention of which no satisfactory method has been devised. Fortunately, 

 the shrinkage usually produces no distortion. 



4. BOUIN'S FLUID. 



Formula: Picric acid, saturated aqueous solution 225 c.c. 



Formalin ' 75 c.c. 



Glacial acetic acid ; , 15 c.c. 



Specimens are kept in the fluid from two to seven days, not longer, according 

 to their size; transfer to 30 per cent alcohol for one hour, to 50 per cent alcohol 

 for from one to two hours, to 60 per cent alcohol for twelve hours, and finally to 70 

 per cent alcohol, which must be changed daily until it no longer shows even a 

 trace of yellow discoloration by picric acid. 



5. MULLER'S FLUID. 



Formula: Bichromate of potassium 20 gm. 



Sulphate of sodium 10 gm. 



Water 1000 c.c. 



Miiller's -fluid is a valuable reagent, and for the study of the later stages of the 

 nervous system indispensable. The objections to its use are that it requires a 

 long time to act, that it renders the specimens brittle, and makes them somewhat 

 difficult to stain. It must be used in large quantities and be frequently changed, 

 and allowed to act on the specimens from three to eight weeks, according to their 

 size. The appearance of a film or scum indicates that the fluid needs to be changed. 



6. PARKER'S FLUID. 



Formula:* 70 per cent alcohol . 100 c.c. 



Formaldehyde i c.c. 



Very convenient when a simple and expeditious preservative is necessary. The 

 specimens are placed in the fluid, which ought to be renewed in a few hours. 

 They may be kept permanently in the fluid, but it is desirable, before using them 

 for study, to remove the formaldehyde by treating them with fresh 70 per cent 

 alcohol. 



7. FLEMMING'S FLUID. 



Formula: i per cent solution of chromic acid . . . . 50 c.c. 



2 per cent solution of osmic acid j2 c.c. 



Glacial acetic acid 3 c.c. 



This fluid must be used freshly mixed, and must not be kept in the dark. The 

 specimens must be of small size and as fresh as possible. The amount of fluid 

 used should be not less than 15 times the volume of the specimen. Speci- 

 mens are kept in the fluid from twenty-four to forty-eight hours, washed in 

 running water from four to twenty-four hours, and then transferred to alcohols 

 of gradually increasing strength. The fluid is useful chiefly for cytological work. 



* Differs slightly from the original formula. 



