260 BACTERIOLOG Y. 



reverse is the case. The objections to this method 

 are : " First. 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 subsequent experiment may, by 

 its immunity from the effects of the pathogenic test- 

 organism, give rise to the mistaken assumption that 

 this had been destroyed by the action of the germicidal 

 agent to which it had been subjected." (Sternberg.) 



DETERMINATION OF ANTISEPTIC PROPERTIES. 



For this purpose 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 the substance to be tested is to be added in dif- 

 ferent 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 volatile nature or not injured by heat, the 

 tubes may then be sterilized. After this they are to be 

 inoculated with the organism with 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 



