THE MICROSCOPE. ioj 



Glass funnels should be used to protect the fingers in filtering 

 the stains. Sections of hardened tissues are treated in the same 

 manner, with the necessary modifications, and the bacillus is shown 

 by this method equally well in specimens hardened in spirits or 

 chromic acid. 



In a later number of the Journal William Vignal, College de 

 France, writes of the Ehrlich method, and says the details are very 

 precise, but the following may be added to them with advantage: 



1. It is desirable to keep the staining fluid with the cover- 

 glass, during a quarter of an hour, at a temperature of 140" Fahr. 

 The coloring matter penetrates more thoroughly and the bacilli are 

 more deeply and equally colored. 



2. It is not advisable to mount the preparations in water, but 

 in a solution of gum mixed with glycerine, prepared in the following 

 manner: Equal parts of neutral glycerine and filtered solution of 

 gum are mixed together ; the gum is of the same thickness as the 

 glycerine, and should be, before mixing, heated in a water-bath with 

 a small quantity of arsenious acid, in order to prevent the develop- 

 ment of fungi. 



3. Aniline dyes are apt to fade very quickly. 



4. The tissues from which the sections are made should be 

 hardened in alcohol only. Chromic and picric acid, also salts of 

 chromic acid, prevent the staining of the bacillus. This method of 

 staining is based on the theory that the tubercle-bacillus is enclosed 

 in a sheath, which, by alkalies, is softened and penetrated (aniline 

 water is a liquid alkali), but is hardened by contact with acids. 

 Nitric acid combines with the coloring matter of aniline to form 

 colorless and soluble salts ; this acid is thus effectual in removing 

 the color from the other elements of the tissue not required to be 

 stained. 



It happens frequently that physicians desire to ascertain 

 whether tubercles contain the bacillus, but they have not the time 

 for making sections. In such cases the following methods may be 

 adopted: divide the tubercle with a bistoury, then scrape one of the 

 surfaces, spread the scraping on a cover-glass, and treat them in the 

 same way as the sputum. In preparations thus made, there are 

 very few isolated bacilli. They are present in clusters, and exam- 

 ined by a low microscopic power represent red or blue spots, but 



