8 HISTOLOGICAL TECHNIC 



should be changed after a few hours. Fixation with Orth's fluid 

 gives an excellent basis for a hsematoxylin-eosin stain (see (i), p. 20). 

 The fixative should always be freshly prepared. It is convenient to 

 keep the 8-per-cent. formalin solution and the double-strength 

 Miiller's fluid in stock. Orth's fluid is then prepared by simply tak- 

 ing equal parts of each. 



(7) Osmic Acid. — This, in a i-per-cent. aqueous solution, is a 

 quick and excellent fixative of poor penetrating power. Very small 

 pieces of tissue must therefore be used. They should remain in the 

 fluid from twelve to twenty-four hours. Osmic acid stains fat and 

 myelin black and is consequently useful in demonstrating their 

 presence in tissues. Fixation should take place in the dark. 



(8) Flemming^s Fluid. 



Chromic acid, i-per-cent. aqueous solution, 25 c.c. 



Osmic acid, i-per-cent. aqueous solution, 10 c.c. 



Glacial acetic acid, i-per-cent. aqueous solution, 10 c.c. 



Water, 55 c.c. 



Flemming's fluid is one of the best fixatives for nuclear structures, 

 and is of especial value in demonstrating mitotic figures. Very 

 small pieces of tissue should be placed in the fixative, where they 

 remain for from twenty-four hours to three days. The solution 

 should be freshly made as required, or a stock solution without the 

 osmic acid may be kept, and the latter added at the time of using. 



(9) Mercuric Chlorid. — This may be used either in saturated 

 aqueous solution or in saturated solution in 0.75-per-cent. salt solu- 

 tion. Fixation is complete in from twelve to twenty-four hours, 

 and is usually very satisfactory. 



A saturated solution of mercuric chlorid in 5-per-cent. aqueous 

 solution of glacial acetic acid also gives good results. 



(10) Zenker's Fluid. 



Potassium bichromate, 2.5 gm. 



Sodium sulphate, i . o gm. 



Mercuric chlorid, 5 . o gm. 



Glacial acetic acid, 5 . o c.c. 



Water, 100. o c.c. 



This fluid should be freshly made, or the salts may be kept in solution 

 and the acetic acid added at time of using. 



Zenker's fluid is a good general fixative, but usually causes some 

 shrinkage of the tissue elements. Fixation requires from six to 

 twenty-four hours. The most serious drawback to Zenker's fluid 



