METHODS OF TESTING DISINFECTANTS. 617 



Fig. 111. 



This tube, after being plugged at the bottom with 

 glass-wool (a, Fig. Ill), and at its wide extremity 

 with cotton-wool, is placed vertically, 

 small end down, into an Erlenmeyer 

 flask of about 100 c.c. capacity and 

 sterilized in a steam sterilizer for the 

 proper time. It is kept in the 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 de- 

 gree of transparency is reached which 

 will permit the reading of moderately 

 fine print through a layer of the fluid 

 about 2 cm. thick — i. e., through an or- 

 dinary test-tube full of it. This filtrate 

 can then be subjected to the action of 

 the disinfectant. As a rule, the results 

 are more uniform than when no atten- 

 tion is paid to the presence of clumps. 

 It is scarcely necessary to say that in 

 the practical employment of disinfec- 

 tants outside the laboratory no such pre- 

 cautions are taken ; but in laboratory 

 work, where it is desired to determine 

 exactly the value of different substances 

 as germicides, all the precautions men- 

 tioned will be found essential to preci- 



Cylindrical fun- 

 nel used for filtering 

 cultures on which 

 disinfectants are to 

 be tested. 



sion. 



The disinfectant value of gases and vapors is deter- 

 mined bv their action upon test-objects in closed 



