THE FURTHER TREATMENT OF THE SECTION. 39 



added. To prevent decomposition of the fluid a little camphor or sodium 

 salicylate is placed in the mixture. A drop of this fluid is smeared on the 

 slide or cover-slip as evenly and thinly as possible. A section or a series 

 of sections arranged in their proper sequence is then placed upon the slide 

 so prepared. Any folds in the section are smoothed out with a brush, and 

 the section or the whole series gently pressed down upon the glass. When 

 the desired number of sections are on the slide or cover-slip, they are 

 warmed over a small spirit or gas flame until the paraffin is melted. At 

 the same time the albumen coagulates. The sections are now fixed, and 

 are loosened from the glass only when agents are used which dissolve 

 albumen, as, for instance, strong acids, alkalies, and certain staining 

 fluids. If it is desired that a given space, say the size of a cover-slip, be 

 filled up with sections as far as possible, an outline of the cover-slip to be 

 used may be drawn upon a piece of paper and placed under the slide in 

 the required position. 



A second and in many respects better method is the fixation of 

 the section with distilled water (Gaule). The paraffin sections are 

 spread in proper sequence on a thin layer of water placed on the slide. 

 There should be sufficient water to float the sections. The slide is then 

 dried in a warm oven kept at 30 to 35 C., or gently heated by holding 

 it at some distance from a spirit or gas flame (the paraffin should not 

 melt). By this treatment the sections are entirely flattened out. The 

 superfluous water is either drained off by tilting or drawn off with blot- 

 ting-paper, the sections are definitely arranged with a brush, and the 

 whole is placed for several hours in a warm oven at 30 to 35 C. The 

 sections thus dried are exposed, over a flame, to a temperature higher 

 than the melting point of the paraffin, and from now on can be subjected 

 to almost any after-treatment. The slide or cover-slip should be thor- 

 oughly cleaned (preferably with alcohol and ether), as otherwise the water 

 does not remain in a layer, but gathers in drops. 



The advantage of this method lies in the fact that the evaporated 

 water can have no possible influence on the subsequent staining of the 

 sections, while albumen, especially if it be in a thick layer, is sometimes 

 stained, thus diminishing the transparency of the preparation. 



This method, although trustworthy for alcohol and sublimate prepara- 

 tions, often fails with objects' that have been treated with osmic acid, 

 chromic acid and its mixtures, nitric acid, and picrosulphuric acid. In 

 such cases advantage may be taken of the so-called Japanese method, 

 which is a combination of the above fixation methods. A little Mayer's 

 albumen is placed on the slide and so spread about that hardly a trace of 

 the substance can be seen. The slide is then put in a warm oven heated 

 to 70 C. This temperature soon coagulates the albumen, after which 

 the sections are fixed to the slide by the water method (Rainke, 95). 

 The procedure can be varied by adding to the distilled water one drop of 

 glycerin-albumen or gum arabic to every 30 c.c. of water (vid. also 

 Nussbaum). 



When a large number of paraffin sections are to be fixed to cover-slips, 

 the following method may be recommended : A small porcelain evapo- 

 rating dish is nearly filled with distilled water and placed on a stand 

 which elevates it 6 to 8 inches from the table. A number of sec- 

 tions are placed on the water, which is then heated by means of a gas 

 flame until the sections become perfectly flat, care being taken not to 

 raise the temperature of the water sufficiently to melt the paraffin. Each 



