The following means of fixation are employed.
1. Dry Heat.
A simple plate of copper on a stand is used, under one end of which burns a Bunsen flame. After some time a certain constancy in the temperature of the plate is reached, the part nearest to the flame is hottest, that farther away is cooler. By dropping water, toluol, xylol, etc. on to it, one can fairly easily ascertain that point of the plate which has reached the boiling temperature of the particular fluid.
Far more convenient is Victor Meyer's apparatus, used by chemists. This consists of a copper boiler, modified for our purpose, with a roof of thin copper-plate, perforated for the opening of the vapour tube. Small quantities of toluol are allowed to boil for a few minutes in the boiler, and the copper-plate soon reaches the temperature of 107°-110°.
For the ordinary staining reagents (in watery fluids) it is enough to place the air-dried preparation at about 110° C. for one half to two minutes. For differential staining mixtures, for instance the eosin-aurantia-nigrosin mixture, a time of two hours is necessary, or higher temperatures must be employed.
2. Chemical means.
a. To obtain a good triacid stain, the preparations may be hardened, according to Nikiforoff, in a mixture of absolute alcohol and ether of equal parts, for two hours. The beauty of specimens fixed by heat is however not quite fully reached by this method.
b. Absolute alcohol fixes dried specimens in five minutes sufficiently to stain them subsequently with Chenzinsky's fluid, or hæmatoxylin-eosin solution. It is an advantage in many cases, especially when rapid investigation is required, to boil the dried preparation in a test-tube in absolute alcohol for one minute.
c. Formalin in 1% alcoholic solution was first used by Benario for fixing blood preparations. The fixation is complete in one minute, and the granulations can be demonstrated. Benario recommends this method of fixing, especially for the hæmatoxylin-eosin staining.
These methods are described as the most suitable for blood-investigation in general. For special purposes, for instance, the demonstration of mitoses, blood platelets, etc., other hardening reagents may be used with advantage: Sublimate, osmic acid, Flemming's fluid, and so forth.