197 



TESTING OF DISINFECTANTS. 



In studying the action of physical and chemical agents 

 on bacteria it is necessary to rigidly adhere to certain re- 

 quirements without which the results would be of little 

 value, if not wholly contradictory. The conditions which 

 underly.the testing of disinfectants may be summed up as 

 follows. 



(1 ). Variable resistance of spores and of the vegetat- 

 ing forms of one and the same organism. It has been 

 shown in recent years that considerable variation may exist 

 in the resistance which an organism possesses to destruc- 

 tion. Thus, while there are some spores of anthrax which 

 are readily destroyed by steam-heat, 100 C., others have 

 been known to withstand this temperature for 10-12 min- 

 utes. Again it was formerly stated that anthrax spores 

 were destroyed by 5 per cent, carbolic acid in two days 

 but the researches of Fraenkel have shown that spores of 

 anthrax may be had which are not destroyed by an ex- 

 posure of 30 to 40 days. In view of these facts several 

 standards have been proposed. Thus Fraenkel designates 

 anthrax spores which are destroyed by 5 per cent, carbolic 

 in less then 10 days as feebly resistant; in 10 to 20 days 

 as of average resistance; in 20 to 30 days as very resistant; 

 in 30 to 40 days as extremely resistant. Geppert's stand- 

 ard an fchiMX sp)t35rir e those which are infectious after 

 boiling for one minute 1 c. c. of a spore suspension which 

 is added to 30 c. c. of boiling water. Esmarch has sug- 

 gested as a standard anthrax spores which when fixed on 

 silk threads resist steam-heat of 100 G. for 10 minutes. 



(2). The influence of the medium in which the organ- 

 ism is tested. Thus it has been shown that to destroy an- 

 thrax spores in bouillon it requires'20 tin)3s as much mer- 



