117 



of the possibility of infection. In any case, great care should be observed 

 in making the mounts. The slides, covers and needle used must be steril- 

 ized, every antiseptic precaution must be observed; and avoid placing an 

 excess of the material on the slide. As soon as the observation is com- 

 pleted (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. 



FIG. 43. Jeffer's circular counting plate for Petri dish cultures. The entire area (100 

 sq. cm.) is marked off into ten equal sectors of ten sq. cm. each. 



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. 



