EXPERIMENTS. 255 



sive sublimate in 1 : 1000 solution, under different con- 

 ditions — with and without the presence of albuminous 

 bodies other than the bacteria and under varying condi- 

 tions of temperature. 



In making these experiments be careful to guard 

 against the introduction of enough sublimate into the 

 agar-agar from which the Petri plate is to be made to 

 inhibit the growth of the organisms which may not have 

 been destroyed by the sublimate. This may be done by 

 transferring two drops from the mixture of sublimate 

 and organisms into not less than 10 c.c. of sterilized salt 

 solution in which they may be thoroughly shaken for 

 from one to two minutes, or into the solution of am- 

 monium sulphide of the strength given. 



To 10 c.c. of a bouillon culture of staphylococcus 

 pyogenes aureus, or anthrax spores, add 10 c.c. of corro- 

 sive sublimate in 1 : 500 solution, and allow it to re- 

 main in contact with the organisms for only one-half the 

 time necessary to destroy them (use an organism for 

 which this has been determined under these conditions). 

 Then transfer a drop of the mixture to each of three 

 liquefied agar-agar tubes and pour them into Petri 

 dishes. Place them in the incubator and observe them 

 for twenty-four, forty-eight, and seventy-two hours. 

 No growth occurs. How is this to be accounted for ? 



At the end of seventy-two hours inoculate all of these 

 plates with a culture of the same organism which has 

 not been exposed to sublimate, by taking up bits of the 

 culture on the needle and drawing it across the plates. 

 A growth now results. We have here an experiment in 

 which organisms which have been exposed to sublimate 

 for a much shorter time than is necessary to destroy 



