200 



tubes should be kept under observation for 1 2 3 weeks 

 before definite conclusions can be drawn. 



(8). Temperature at which the trial inoculation 

 tubes are kept. The organism which has been exposed to 

 the action of the disinfectant should be placed under con- 

 ditions which are most favorable to its growth. That is, 

 the best nutrient medium and the most suitable tempera- 

 ture should be furnished. Transplantations made into gel- 

 atin and kept at ordinary room temperature frequently 

 fail to grow while parallel bouillon and agar cultures, kept in 

 the incubator,develop. It is therefore desirable to make the 

 transplantation onto the surface of inclined agar tubes or 

 into bouillon and to keep the tubes under observation at a 

 temperature of about 37.5 C. for two or three weeks. 



(9). Negative experiments with animals inoculated 

 with organisms exposed to heat, or to the action of chemi- 

 cals prove nothing. The organism may be dead or it may 

 have become attenuated and is therefore without action, 

 although it may still grow on artificial media. Thus, an- 

 thrax spores exposed to the boiling temperature for 2 min- 

 utes no longer kill guinea-pigs, but nevertheless can grow 

 in tubes, even after 5 minutes exposure. Again, positive 

 experiments may be obtained by inoculating white mice or 

 guinea-pigs with the mixture of bacteria and disinfectant at 

 a time where transplantation of a corresponding amount on 

 a nutrient medium fails to grow owing to the antiseptic 

 power of the disinfectant carried over. 



METHODS FOR TESTING DISINFECTANTS. 



(1). . Silk threads. This method was introduced by 

 Koch and has been extensively used. Threads of silk, linen, 

 or cotton are cut up into lengths of about 1 cm. They are 

 placed in a sterilized plugged test-tube and sterilized in 

 the dry-heat oven. A cloudy suspension of the spores or 

 bacteria to be tested is made in sterilized water. The 

 pieces of sterilized threads are immersed in this suspen- 

 sion for some minutes, then transferred with sterilized for- 



