Zanker's Fluid

ZANKER'S FLUID, a very common fixative used in histological technique. The composition of Z. fluid is as follows: mercuric chloride 5.0, potassium dichromate 2.5, sodium sulfate 1.0, distilled water 100.0 cm^g (without mercuric chloride — Muller's fluid). To this mixture, before use, 5 cm³ of ice-cold acetic acid is added. Although Z. fluid penetrates tissues satisfactorily, it is desirable that the pieces be cut as thinly as possible. Fixation is carried out for 12-18 hours. Then follows washing in running water (24 hours), after which it is necessary to free the tissues from excess mercuric chloride and its precipitates; for this the following procedure is adopted. The pieces are placed in 70° alcohol, stained with iodine tincture to a brownish-red hue (Mader color). After a certain time the iodized alcohol becomes decolorized, acquiring a yellowish tint. Then the pieces are transferred to another portion of alcohol with iodine, and so on until the iodized alcohol ceases to become decolorized. After this the pieces are passed through a series of alcohols and embedded in collodion or paraffin. If precipitates of mercuric chloride remain on the sections, the latter are washed for a few minutes in alcohol with iodine, and then in pure alcohol. If the sections have yellowed, the excess iodine is washed out in a ¹/₄% solution of hyposulfite with subsequent washing in several portions of pure water. Z. fluid fixes nuclei and karyokinetic figures, as well as protoplasm and its derivatives, excellently. Fixation with Z. fluid is of particular importance for the processing of blood-forming organs, as it makes it possible to very selectively reveal the granulation and various shades of coloration of the protoplasm of blood cells. Among the disadvantages of fixation with Z. fluid should be noted: 1) the difficulty, and sometimes the impossibility, of preparing sections by the freezing method; 2) the difficulty, and sometimes the impossibility, of revealing fat and lipoids. A good modification of Z. fluid is Zanker-formol (Helly's fluid, in which acetic acid is replaced by formalin).

A. Koeitner.