286 HISTOLOGICAL TECHNIQUE. 



After fixation in Mailer's fluid specimens should be washed in 

 running water over night, or for twenty-four hours, and then hard- 

 ened in alcohols of progressively greater strengths. While in the 

 weaker alcohols specimens should be kept in the dark, to avoid 

 the formation of precipitates, which occur under the influence of 

 light. Pieces of tissue placed in Midler's fluid should not be more 

 than 1 cm. in thickness. 



Two excellent modifications of Midler's fluid have been devised 

 by Zenker and Orth for the purpose of hastening the fixation and 

 of securing a more faithful preservation of structural detail. 



2. Zenker's Fluid. — 



To this stock solution 5 per cent, of glacial acetic acid is to be 

 added just before use of the fluid. 



Zenker's fluid fixes tissues in from three to twenty-four hours. 

 The pieces should not be more than 5 mm. thick, and after fixa- 

 tion should be washed for several hours in running water and then 

 hardened in alcohol. 



This solution possesses the disadvantage that a precipitation of 

 mercury or some mercurial compound is likely to take place within 

 the tissues. This deposit may be, at least in great measure, removed 

 from the tissues by adding a little tincture of iodine to the harden- 

 ing-alcohols. The iodine combines with the mercury and produces 

 a soluble compound, which is dissolved out by the alcohol. As the 

 iodine disappears from the alcohol the latter becomes bleached, and 

 fresh tincture must be added until the alcohol remains permanently 

 tinged. If, after sections of the tissue have been prepared, they 

 are found to contain a mercurial deposit, this can be removed by 

 treatment with dilute iodine tincture or with Lugol's solution. 



3. Orth's Fluid.— 



Potassium bichromate, 2.5 grams. 



Sodium sulphate, 1 gram. 



Distilled water, 100 cc. 



This stock solution is Miiller's fluid. Before use, 10 cc. of for- 



