BACTERIOLOGICAL TECHNIC. 9 1 



the cover-glass and mounting like the hanging drop. The bacteria will be 

 found close to the cover-glass. 



Bacteria can be examined mounted in water on a slide coveredjvith cover- 

 glass, in order to make observations regarding motility. Of course it is not 

 desirable to examine pathogenic microbes in this manner because of the pos- 

 sibility of infection. In any case, great care should be observed in making 

 the mounts. The slides, covers and needle used must be sterilized, every 

 antiseptic precaution must be observed; and avoid placing an excess of the 

 material on the slide. As soon as the observation is completed (few minutes 

 to half an hour) the mount (slide cover and all) should be placed in a 5 per 

 cent, solution of carbolic acid preparatory to cleaning. 



Cover-glass preparations, temporary and permanent, are made as 

 follows: 



a. Clean a cover-glass thoroughly, dry it well and heat it. The heating 

 will cause the smear to spread better and to adhere better. The slides to 

 be used must also be clean and dry. 



b. By means of the platinum needle, spread a bit of the bacterial growth 

 or culture over the greater portion of the surface of the cover-glass. Add a 

 droplet of water, if desired, to separate the bacteria more. Spread evenly. 

 Do not use too much material, as it will make an unsightly mount. 



c. Air-dry the smear preparation. This requires but little time, perhaps 

 a minute or two. 



d. Pass the cover-glass preparation through the flame of a Bunsen burner 

 four times. This must not be done too slowly as that will char or burn the 

 microbes, nor yet too quickly, as that would not coagulate the albuminous 

 matter and thus fail to fix the microbes upon the cover-glass. A little ex- 

 perience will soon teach the proper speed. Four seconds, or a little less, is 

 the average time in which to make the four passages through the flame. 



e. Place a drop or two of the stain on the fixed smear and allow it to act 

 long enough to stain sufficiently, holding the cover-glass over a flame to 

 warm the preparation. Do not heat it more than 60 to 70 C. On an 

 average the stain will be sufficiently deep in five minutes. Fuchsin requires 

 longer time than does methyl-blue or gentian- violet. 



f. Wash off the excess of the stain under a small hydrant stream or by 

 means of a wash bottle, or by moving it about in a dish of water. 



g. After washing, the preparation may be examined as a temporary water 

 mount. If it is satisfactory it may be made a permanent mount by turning 

 the cover-glass up again and allowing the water to evaporate and then 

 mounting in Canada balsam with xylene, oil of cloves or some other diluent 

 for Canada balsam. Oil of cloves acts on the stain for which reason xylene, 

 benzene or some other balsam diluent of the coal-tar series is preferable. 

 Special staining methods have already been explained. The above is a 



