450 BACTERIOLOGY. 



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

 regards reproductive activity without being killed ; and 

 in this case a modified fijrm 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 OP ANTISEPTIC PEOPEETIES. 



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 volatile nature or not injured by heat, they 

 may then be sterilized. After this they are to be in- 

 oculated 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 



