DESTE UCTION OF BA GTEEIA B Y CHEMICALS. 1 53 



few drops of the culture from which all lumps have 

 been filtered are added. At intervals of one, five, ten, 

 fifteen, and thirty minutes, one hour, and so on, a small 

 platinum loopful of the mixture is taken from each tube 

 and inoculated into 10 c.c. of lukewarm gelatin, from 

 which plate cultures are made. The results obtained are 

 signified as follows : x per cent, of the disinfectant in 

 watery solution and at x temperature kills the organism 

 in twenty minutes, y per cent, kills in one minute, and 

 so on. If there be any doubt whether the trace of the 

 disinfectant carried over with the platinum loops may 

 have rendered the gelatin unsuitable for growth, thus 

 falsifying results, control cultures should be made with 

 vigorous bacteria in gelatin to which a similar trace of 

 the disinfectant has been added. 



The disinfectant to be examined should always be 

 dissolved in an inert fluid, such as water; if on account 

 of its being difficultly soluble in water, it is necessary 

 to use alcohol for its solution, control experiments may 

 be required to determine the action of the alcohol on the 

 organism. Sometimes, as in the case of corrosive sub- 

 limate, the chemical unites with the cell substance to 

 form an unstable compound, which inhibits the growth 

 of the organism only while the union exists. In some 

 tests it is necessary to break up 'this union and note 

 then whether the organism is alive or dead. 



In the above determinations the absolute strength of 

 the disinfectant required is considerably less when cul- 

 ture media rich in albumin are employed than when the 

 opposite is the case. Thus creoliu (Pearsons), when 

 bouillon is used as a culture medium, stops develop- 

 ment in the proportion of 1 to 15,000 or 1 to 5000; 

 when ox -serum is used only in the proportion of 1 to 



