EXAMINATION OF LIVING BACTERIA. 21 



vessels should be carefully cleansed. This is most 

 successfully 'accomplished with a solution of corrosive 

 sublimate, 1 : 1000 (it is advisable to have a solution 

 of this strength always handyj as it is in constant 

 use).i A piece of filter-paper, soaked in this solution, 

 is then placed at the bottom of the dish, and the 

 piece of turnip or potato is placed upon it, the same 

 side as before being uppermost. The upper glass is 

 then put over, and the vessel is kept at the temper- 

 ature of an ordinary sitting-room. After a few days 



Fig. 1. 



small variously shaped masses appear on the slice in 

 the form of little droplets, dry flat scales, or more 



' In the use of corrosive sublimate as a sterilising agent, 

 it is of importance to remember not to use more of the solu- 

 tion than is absolutely necessary, lest so much of the salt 

 should be left adhering to the sides of the dish, after the 

 water has evaporated, that it may fall on the culture and kill 

 the bacteria. It is further necessary to bear in mind the fact, 

 that, if albuminous substances come into contact with the 

 corrosive sublimate solution, the mercury is precipitated, 

 and thus the sterilising properties of the solution are more or 

 less destroyed. For these reasons it is advisable to sterilise 

 by means of heat whenever possible. 



