Methods of Deterinination of Pathogenic Microbes. 109 



placed upon the slide in such a manner that the bal- 

 sam distributes itself between the two glasses. 



"We can omit having recourse to clearing (clove oil, 

 cedar oil, etc.), and, after drying, pass directly to the 

 balsam; but it is incontestable that, if this practice 

 increases a little the duration of the work, it also 

 gives more distinctness to the preparation. 



Sections. — Stained sections must also be dehydrated 

 in order to be mounted in balsam. For this purpose 

 they are passed successively through specimens of 

 alcohol of different strength, ending with absolute al- 

 cohol (70, 90, 100 per cent). They are then cleared 

 by immersing them in one of the substances men- 

 tioned above (cedar oil, bergamot oil, clove oil), then 

 placed in xylol, and, finally, on a drop of balsam 

 which has previously been deposited on a slide and 

 which is now at once covered by the cover glass. 



These diverse operations may be made upon the 

 slide itself, the stained section having been spread 

 and fixed at the start by a semi-desiccation. This 

 last is easily accomplished either by the aid of filter 

 paper which is used to absorb the water from the 

 section, or by moderate heating. 



Methods of single staining. 



Hydro-alcoholic solutions of aniline colors. — These are 

 made extemporaneously by adding a few drops of 

 a saturated alcoholic solution of the dj^e to a watch 

 glass of distilled water. They are largely used for 

 single staining, especially for cover glasses. This 

 method is sulficient for a rapid examination, when 

 the object is merely to determine the presence or ab- 

 sence of microbes in the preparation. 



