TESTING OP DISINFECTANTS. 519 



1. — Variable resistance of spores and of the vegetating 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 destruction. Thus, while 

 there are some spores of anthrax which are readily de- 

 stroyed by steam-heat (100°) others have been known to 

 withstand this temperature for 10-12 minutes. Again, it 

 was formerly stated that anthrax spores were destroyed by 

 5 per cent, carbolic acid in two days but the researches of 

 Praenkel have shown that spores of anthrax may be had 

 which are not destroyed by an exposure of 30 to 40 days or 

 even longer. 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 than 

 10 days as feebly resistant; in 10 to 20 days as of aver- 

 age resistance; in 20 to 30 days as very resistant; in 30 to 40 

 days as extremely resistant. Geppert's standard anthrax 

 spores are 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 suggested as a standard, 

 anthrax spores which when fixed on silk threads resist 

 steam-heat of 100° for 10 minutes. 



2. — The influence of the medium in which the organism is 

 tested. Thus, it has been shown that to destroy anthrax 

 spores in bouillon it requires 20 times as much mercuric 

 chloride (1-1000) than when they are suspended in water; 

 and, 250 times as much are necessary when they are dis- 

 tributed in blood-serum. 



3. — The temperature at which the disinfection is made. 

 The higher the temperature at which the experiments are 

 made the more rapid and energetic will be the action of the 

 disinfectant. Cholera bacteria are not destroyed by mer- 

 caric chloride (1-1000) in one hour at - 3°, whereas at 36° 

 they are killed in a few minutes. 



