122 THE AMERICAN MONTHLY [Apr 



Upon examination the preparation should be free from 

 deposits or stained back ground. The bacteria should, as 

 a rule, be isolated and distinct, unless they are, the prepa- 

 rations are not satisfactory. 



Cover-glass preparations of bacteria are permanently 

 mounted in the same manner as similar preparations 

 made from the blood or other tissues in histology, the 

 process being to place a drop of the balsam on the center 

 of the slide and place the preparation, film downward, 

 over it and apply slight pressure. Label the preparation, 

 giving the name of the organism, its source, (kind of 

 culture, tissue, etc., from which the preparation was 

 made), stain used, and date. If the specimen is not pre- 

 served, the slide and cover-glass should be cleaned for 

 future use. 



Suggestions Concerning the Microscopic Examination of 

 /Stained Preparations of Bacteria. — In the examination 

 of the bacteria in the stained condition the followiugpoints, 

 and perhaps others, should be observed and noted. (1) 

 Concerning their morphology. Are they spherical, rod- 

 shaped, or spiral ? Are they separated or united in clumps 

 or chains ? If rod- shaped, are the ends pointed, round, 

 or square ? Are the bacteria all of the same form and 

 size ? Note the presence or absence of spores and cap- 

 sules. (2) Concerning their reaction to staining fluids. 

 Do they stain uniformly or irregularly ? Do they stain 

 deeply or faintly ? Is the ceuter lighter than the periph- 

 ery ? Is there an unstained central band and deeply 

 stained ends (polar stain)? Do all the bacteria take the 

 stain alike ? 



Staining 8olulio7is. — The basic aniline dyes are used in 

 staining bacteria. There is a large number of these, and 

 there are several formulae for preparing staining solu- 

 tions from each. Further, as will be seen from the chap- 

 ters on staining bacteria in the text-books, there are sev- 

 eral methods of applying these stains. In an introduc- 



