290 APPLIED BACTERIOLOGY 



respective standard solutions. These are allowed to remain 

 at the temperature of the room, preferably 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 determined. 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 ; 



