TESTING DISINFECTANTS. AND ANTISEPTICS. 449 



The whole tube, after being plugged at the bottom 

 of its wide part with glass wool and at its wide open 

 extremity with cotton wool, is placed vertically, small 

 end down, into an Erlenraeyer flask of about 100 c.c. 

 capacity and sterilized in a steam sterilizer for the 

 proper time. It is kept in the covered sterilizer until 

 it is to be used, which should be as soon as possible 

 after sterilization. 



The watery suspension or bouillon culture of the 

 organisms is now to be filtered repeatedly through the 

 glass wool into sterilized flasks until a degree of trans- 

 parency is reached which will permit the reading of 

 moderately fine print through a layer of the fluid of 

 about 2 cm. thick, i.e., through an ordinary test-tube 

 full of it. It can then be subjected to the action of 

 the disinfectant, and, as a rule, the results are far more 

 uniform than when no attention is paid to the exist- 

 ence of clumps. It is hardly necessary to say that in 

 the practical employment of disinfectants outside the 

 laboratory no such precautions are taken, but in lab- 

 oratory work, where it is desirable to determine exactly 

 the value of different substances as germicides, all the 

 precautions that have been mentioned will be found 

 essential to success. 



In determining the germicidal value of different 

 chemical agents upon certain pathogenic bacteria, sus- 

 ceptible animals are sometimes inoculated with the 

 organisms after they have been exposed to the disinfec- 

 tant. If no pathological condition results, disinfection is 

 presumed to have been successful, while if the condition 

 characteristic of the activities of the given organism in 

 the tissues of this animal appears, the reverse is the case. 

 The objections to this method that have been raised 



