EXPERIMENTS. 521 



If, for example, there was no development in the tubes 

 in which the antiseptic was present in the proportion 

 of 1 : 1000 and growth in the one in which it was 

 present in 1 : 1400, the experiment would be repeated 

 with streDgth of the antiseptic corresponding to 1 : 1000, 

 1 : 1100, 1 : 1200, 1 : 1300, 1 : 1400, and in this way one 

 gradually strikes the point at which growth is just pre- 

 vented. This point represents the antiseptic value of 

 the substance used for the organism upon which it has 

 been tested. 



EXPERIMENTS. 



Into each of three tubes containing 10 c.c. one of 

 normal salt-solution, another of bouillon, a third of fluid 

 blood-serum add as much of a culture of the staphylo- 

 coccus pyogenes aureus as can be held upon the looped 

 platinum needle. Mix this thoroughly, so that no clumps 

 exist, and then add exactly 10 c.c. of 1 : 500 solution of 

 corrosive sublimate. Mix it thoroughly, and at the 

 end of three minutes transfer a drop from each tube 

 into a tube of liquefied agar-agar, and pour this into a 

 Petri dish. Label each dish carefully and place them 

 in the incubator. Are the results-the same in all the 

 plates? How are the differences to be explained? To 

 what strength of the disinfectant were the organisms 

 exposed in the experiment ? 



Into each of two tubes containing 10 c.c. the one 

 of normal salt-solution, the other of bouillon add as 

 much of a spore-containing culture of anthrax bacilli 

 as can be held upon the loop of the platinum wire. 

 Mix this thoroughly so that no clumps exist, and then 

 add exactly 10 c.c. of a 1 : 500 solution of corrosive 

 sublimate. Mix thoroughly, and at the end of five 



