142 BACTERIOLOGY. 



only when they come in contact with ferment- 

 able substances under proper conditions, and 

 produce illness and disease only when predis- 

 position toward disease exists. Such liability 

 or predisposition we may either inherit from 

 others or acquire by faults of our own. Where 

 no susceptibility to disease exists, we may 

 harbor the bacillus with impunity. We should, 

 then, revile the malicious bacteria no longer, but 

 take ourselves to task and mend our own ways. 

 Not that, some measure of reform having been 

 effected, we should behave ourselves irration- 

 ally for eleven months in the year, then go to 

 a medical Tetzel and have prescribed as in- 

 dulgence a four weeks' sojourn at a watering- 

 place. It is better for the majority of men to 

 put themselves, through sensible ways of liv- 

 ing, into such a condition that bacteria can get 

 no lodgment in their system. This, in few 

 words, is the practical lesson of bacteriological 

 discoveries, Koch to the contrary notwithstand- 

 ing. It is a less comfortable doctrine, but it is 

 scientifically more nearly correct than the 

 other. 



The action of environment upon bacteria 

 may be still further considered. If a bacter- 

 ium that produces disease or that causes fer- 

 mentation or that forms pigment be cultivated 

 for a long time under conditions in which it 



