DETERMINA TION OF ANTISEPTIC PR OPERTIES. 47 1 



are : "Mrst. The test organisms may be modified as 

 regards reproductive activity without being killed ; and 

 in this case a modified form of the disease may result 

 from the inoculation, of so mild a character as to escape 

 observation. Second. An animal that has suffered this 

 modified form of the disease enjoys protection, more or 

 less perfect, from future attacks, and if used for a subse- 

 quent experiment may, by its immunity from the effects 

 of the pathogenic test organism, give rise to the mis- 

 taken assumption that this had been destroyed by the 

 action of the germicidal agent to which it had been sub- 

 jected." (Steruberg.) 



DETERMINATION OF ANTISEPTIC PROPERTIES. 



In this test sterile media are employed and are usually 

 arranged in two groups : the one to remain normal in 

 composition and to serve as controls, while to the other 

 is to be added the substance to be tested in different but 

 known strengths. It is customary to employ test-tubes 

 each containing an exact amount of bouillon, gelatin, or 

 agar-agar, as the case may be. To each tube a definite 

 amount of the antiseptic is added, and if it is not of a vola- 

 tile nature or not injured by heat, they may then be ster- 

 ilized. After this they are to be inoculated with the 

 organism upon which the test is to be made, and at the 

 same time one of the " control " tubes (one of those to 

 which no antiseptic has been added) is inoculated. They 

 are all then to be placed in the incubator and kept under 

 observation. If at the end of twenty-four, forty-eight, 

 or seventy-two hours no growth appears in any but the 

 " control " tubes, it is evident that the antiseptic must 

 be added in smaller amounts, for we are to determine the 



