140 BACTERIOLOGY. 



employed. The ordinary method of cover-slip exam- 

 ination of bacteria, constantly in use in these studies, is 

 performed in the following way: 



Cover-slip Preparations. — 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 essential 

 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 which 

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

 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, then treated 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 acid or sulphuric 

 acid. They are removed from the acid after several 

 days, rinsed off in water, and treated as above. Knauer 

 has recently suggested the boiling of soiled cover-slips 

 and slides for from twenty to thirty minutes in a 10 per 

 cent, watery solution of lysol, after which they are to 

 be carefully rinsed in water until all trace of the lysol 

 has disappeared. They are then to be wiped dry with 

 a clean handkerchief. 



Loeffler'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, then rinse them in 



