41 8 BACTERIOLOGY. 



that favor disease, and in part also that against 

 the faulty social conditions that operate to this 

 end. It is primarily due to the adoption of 

 such measures that civilized states are not now 

 seriously threatened by diseases like cholera. 

 The betterment of the subsoil by drainage 

 or canalization, and the various modes of re- 

 moval or destruction of the waste products of 

 human life and habitation have increased the 

 healthfulness of our dwellings and improved 

 the quality of that indoor climate to which city 

 dwellers are inevitably exposed much of the 

 time. Those substances whose soluble or gas- 

 eous decomposition products are offensive and 

 diminish our capacity for resistance to disease 

 are removed from our vicinity. The intro- 

 duction into the animal body of soluble pro- 

 ducts of putrefaction at the same time with 

 infective material favors infection even in ex- 

 periments upon animals ; with such assistance 

 germs less virulent than the normal are able 

 to bring about infection, and attenuated germs 

 become again infective. Attempts to prove by 

 animal experiments that the gaseous products 

 of putrefaction have a similar effect have not 

 wholly succeeded. But there is this to be re- 

 membered, namely, that the animals used in our 

 experiments are accustomed to a very different 

 atmosphere from that which we ourselves 



