BACTERIA. 253 



may certainly be used with some success in the investiga- 

 tion of the minute structure of the bacterial cell. Their 

 use may generally be successfully carried out by Overton's 

 method. But it should be noted that the membranes of the 

 Bacteria are characterized by relatively great impermeabil- 

 ity. It has been shown by A. Fischer (II, 72) that \% osmic 

 acid and a \% solution of corrosive sublimate, in particular, 

 cause only an incomplete fixation of bacterial cells. 



2. Sections. 



465. Absolute alcohol is commonly used for fixing Bac- 

 teria within infected organisms, pieces of the tissue being 

 placed directly in it. The microtome should be used for 

 cutting sections from these, after imbedding in paraffine 

 ( 43) or celloidin ( 4Qa). 



III. Staining Methods. 



466. Under this head a number of methods will be de- 

 scribed which can be successfully used, in most cases, for 

 recognizing the presence of Bacteria in a fluid or in a dis- 

 eased organism. Then follows a special description of stain- 

 ing methods for tubercle Bacilli, the spores, and the cilia of 

 Bacteria. 



i. Staining with Loeffler's Methylene Blue. 



467. Loeffler's methylene blue consists of 30 ccm. of a 

 concentrated alcoholic solution of methylene blue arid 100 

 ccm. of an aqueous .01$ solution of caustic potash. It keeps 

 indefinitely. 



With cover-glass preparations, it may be used by care- 

 fully warming the preparation with a few drops of the stain 

 until steam is seen to rise, then washing off the stain with 

 water and drying in the air, without heat. A drop of Cana- 

 da balsam is then placed on a slide, and the cover-glass is 

 placed on it. This method does not give a very deep stain, 

 but often brings out delicate differentiations sharply. 



