1 58 BACTERIOLOG Y. 



teria, constantly in use in these studies, is performed in 

 the following way : 



Cover-slip Peepaeations. — In order that the dis- 

 tribution of the organisms upon the cover-slips may 

 be uniform and in as thin a layer as possible it is es- 

 sential that the slips should be clean and free from 

 grease. For cleansing the slips several methods may 

 be employed. 



The simplest plan with new cover-slips is to immerse 

 them for a few hours in strong nitric acid, after wliich 

 they are rinsed in water, then in alcohol, then etlier, 

 and, finally, they may be kept in alcohol to which a 

 little ammonia has been added. When about to be 

 used they should be wiped dry with a clean cotton or 

 silk handkerchief. 



If the slips have been previously used, boiling in 

 strong soap solution, followed by rinsing in clean warm 

 water, and then treating as above, renders them clean 

 enough for ordinary purposes. 



A method commonly employed is to remove all coarse 

 adherent matter from slips and slides by allowing them 

 to remain for a time in strong nitric or sulphuric acid. 

 They are removed from the acid after several days, 

 rinsed in water, and treated as above. Knauer suggests 

 the boiling of soiled cover-slips and slides for from 

 twenty to thirty minutes in a 10 per cent, watery solu- 

 tion of lysol, after which they are to be rinsed carefully 

 in water until all trace of the lysol has disappeared. 

 They are then to be wiped dry with a clean handker- 

 chief. 



Loffler's method, which provides for the complete 

 removal of all grease, is to warm the cover-slips in con- 

 centrated sulphuric acid for a time and then rinse them 



