404 HISTOLOGY. 



The chief fault of Zenker's fluid is its tendency to form a precipitate of 

 mercuric chloride (corrosive sublimate) within the tissue. The precipitate 

 is dissolved out by the addition of enough tincture of iodine to the 80 per 

 cent, alcohol to give it a mahogany color. The color fades as the iodine 

 combines with the sublimate and it should be renewed until for two days 

 there is no perceptible change in its color. This may require a week or more. 

 Then the tissue is transferred to 80 per cent, alcohol which is renewed as 

 long as it becomes discolored by the iodine. In 80 per cent, alcohol the 

 tissue may remain for months but it gradually deteriorates. The pro- 

 longed action of iodine causes some loss in staining capacity; nevertheless 

 the treatment with iodine is an essential routine part of this method of 

 fixation, and it should be thorough enough to remove the precipitate. 

 The latter appears in sections as dark blotches resembling pigment. They 

 may be dissolved after sections have been cut and attached to the slide by 

 immersing the slide in the iodine solution and then rinsing it in 80 per 

 cent, alcohol. 



Telly esnizcky' 1 's Fluid is employed like Zenker's fluid but since it con- 

 tains no mercuric chloride, the after-treatment with iodine is unnecessary. 

 This fluid is a 3 per cent, aqueous solution of bichromate of potassium to 

 which glacial acetic acid should be added shortly before using (5 cc. of 

 acetic acid to 100 cc. of the solution). Tissues may remain in it for two 

 or more days. The reagent is washed out in running water, and the tissue 

 is transferred to 80 per cent, alcohol. 



Formaline is a 40 per cent, aqueous solution of formaldehyde gas. 

 Ten per cent, aqueous solutions of formaline, which are 4 per cent, solu- 

 tions of formaldehyde, are used for the preservation of small embryos and 

 of various tissues. Small human embryos obtained by practitioners should 

 be placed at once in 10 per cent, formaline and forwarded to an embryological 

 laboratory. Tissues should remain in the 10 per cent, formaline for 24 

 hours or somewhat longer, and then are transferred to 80 per cent, alcohol 

 in which they generally shrink. (Frozen sections may be made from the 

 material taken directly from formaline and rinsed in water.) Instead of 

 transferring the tissue from the formaline to 80 per cent, alcohol, some 

 histologists recommend placing it at once in absolute alcohol for 2 days, 

 after which it is immersed in 80 per cent. Formaline is used as a fixing 

 agent in many solutions, especially the following. 



Orth's Fluid is Muller's Fluid with the addition of formaline. Miiller's 

 fluid is a slow fixing solution, in large quantities of w r hich objects may be 

 left from i to 6 weeks; after washing 4 to 8 hours in running water they are 

 put through graded alcohols in which the tissue is hardened; or the tissue 

 may be both fixed and hardened by remaining in the fluid for six months. 



