378 APPLIED BACTBEIOLOGY 



ably as near 15° C. as possible. At the end of the ten 

 minutes a loopful is inoculated into a flask containing 50 c c. 

 of broth, which is incubated at 37° C. and kept under 

 observation for at least ten days. In each of these processes 

 care must be taken to agitate the mixture so as to 

 thoroughly mix the liquids, and any small bodies of growth 

 or broth substance must either be completely rubbed down 

 till they are not perceptible as solids, or else must be 

 filtered off through sterile slag-wool. Those flasks which 

 remain limpid are those in which the organisms have been 

 killed, and the strengths of disinfectant necessary for use 

 with the particular organisms examined is therefore deter- 

 mined. In the examination of the effect of a disinfectant 

 on spore-bearing organisms, the experiments should be 

 repeated with spores carefully dried in vacuo for some 

 days and suspended in sterile water. In this case the 

 number of organisms per c.c. in the suspension should be 

 noted, and the process then conducted as before, 4- 5 c.c. of 

 suspension being substituted for the broth culture. The 

 object of using so large a quantity of broth is to avoid the 

 inhibition of growth of the organisms through the presence 

 of that quantity of disinfectant which is carried over in the 

 loopful. It has been shown that even in great dilutions 

 some disinfectants will exercise this inhibitive action. 

 Thus, for instance, a solution of 1 in 3,000,000 of perchloride 

 of mercury is stated to have done so. It would not be 

 conclusive to use a smaller quantity of broth instead of the 

 50 c.c, and to transfer to an equal quantity containing 

 living organisms from the original culture a second loopful 

 from the disinfectant solution as a control, because the 

 organisms which have been in contact with the disinfectant 

 solution may have been attenuated in their resistance 

 without having been entirely disinfected ; and in that case 

 the disinfectant contained in the loopful might fail to 



