94- Comparative Power of some Disinfectants. 



may be regarded as almost certain, since it has been actually 

 done in the case of several of them. Unfortunately, we 

 cannot always obtain the virus in substance, so as to 

 operate upon it in that way ; and we are compelled, 

 therefore, to consider the possibility of attacking it when 

 suspended in the atmosphere, or attached to walls or other 

 surfaces in a dried state. That some diseases are con- 

 veyed by means of a dried contagium floating in the air 

 seems to be certain, and therefore in the prevention of 

 many diseases — such as scarlet fever, measles, small- 

 pox — we have to face the problem of aerial disinfection, 

 with all its difficulties. The only experiments made to test 

 the effect of disinfectants, in the form of vapours, on a dried 

 animal contagium, which I have seen detailed, are those on 

 vaccine virus by Drs. Dougall and Baxter. The general 

 result of these was to show that concentrated vapours 

 destroyed the contagious quality of the virus when they 

 operated for a sufficient length of time, just as the same 

 agents in substance robbed fresh liquid vaccine of its power 

 of communicating vaccinia. One other point is necessary 

 again to adduce, and that is that the septic microzymes so 

 abundantly found in ordinary processes of putrefaction are 

 destroyed by the same agents used in nearly the same 

 strength. These preliminary statements have now brought 

 me to the ground and reason of my own experiments. Some 

 of the animal contagia^ as those of scarlet fever, measles, and 

 some others, are almost unknown to us as objects of direct 

 observation ; but we have every reason to assume that they 

 are subject to similar vital conditions with those which have 

 been made the subjects of experiment, and therefore will 

 have their virulence annulled by agents which act in that 

 way, either on septic microzymes or on vaccine virus. My 

 experiments have been made with these septic microzymes, 

 which are always attainable, and whose death or continued 

 existence can be proved with greater certainty than is possible 

 in the case of the animal contagia by the method of inocu- 

 lation, which is always liable to some fallacies. It is known 

 that bacteria of different sorts, and especially these septic 

 organisms, can live and multiply in a perfectly clear solution 

 of certain saline matters, and the mixture known as Cohn's 

 solution is admirably adapted for their cultivation. I used 

 a slight modification of that originally recommended by 

 Professor Cohn, composed of the following ingredients : — ■ 



