DETERMINATION OF DISINFECTANT PROPERTIES 319 



Fig. 65 



meyer flask of about 100 c.c. capacity and sterilized in a 

 steam sterilizer for the proper time. It is kept in the steril- 

 izer until it is to be used, which should 

 be as soon as possible after sterilization. 



The watery suspension or bouillon cul- 

 ture 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 about 2 cm. thick 

 — i. e., through an ordinary test-tube 

 full of it. This filtrate can then be sub- 

 jected to the action of the disinfectant. 

 As a rule, the results are more uniform 

 than when no attention is paid to the 

 presence of clumps. It is scarcely neces- 

 sary to say that in the practical employ- 

 ment of disinfectants outside the labora- 

 tory no such precautions are taken; but 

 in laboratory work, where it is desired 

 to determine exactly the value of different 

 substances as germicides, all the precau- 

 tions mentioned will be found essential 

 to precision. 



The disinfectant value of gases and 

 vapors is determined by their action 

 upon test-objects in closed chambers. 

 The object is to determine the proportion 

 of the gas, when mixed with air, that is 

 required to destroy the bacteria exposed to its action in 

 a given time. For this purpose the test is usually made 



Cylindrical funnel 

 used for filtering cul- 

 tures on which dis- 

 infectants are to be 

 tested. 



