322 APPLICATION OF METHODS OF BACTERIOLOGY 



of the antiseptic; the amount necessary for antisepsis is 

 then a trifle greater than that used in the last tube. 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 should be repeated with strengths of the anti- 

 septic corresponding to 1:1000, 1:1100, 1:1200, 1:1300, 

 1 : 1400, and in this way one ultimately determines the 

 amount by which growth is jiist prevented; this represents 

 the antiseptic value of the substance for the organism with 

 which it was tested. 



EXPERIMENTS. 



To each of three tubes containing 10 c.c. — one of physio- 

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

 blood-serum — add as much of a culture of micrococcus 

 aureus as can be held upon a looped platinum wire. Break 

 this up carefully to eliminate clumps, and then add exactly 

 10 c.c. of a 1 : 500 solution of corrosive sublimate. Mix 

 thoroughly, and at the end of three minutes transfer a drop 

 from each tube into tubes of liquefied agar-agar, and pour 

 these into Petri dishes. 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 ex- 

 posed in the experiment? 



To each of two tubes^the one containing 10 c.c. of 

 physiological salt-solution, the other of bouillon — add as 

 much of a spore-containing culture of anthrax bacilli as can 

 be held upon a loop of platinum wire. Distribute this uni- 

 formly through the medium, and then add exactly 10 c.c. of 

 a 1 : 500 solution of corrosive sublimate. Mix thoroughly. 



