COMBATING PARASITIC BACTERIA. 183 



hands; we should wear only disinfected clothes; 

 we should never put our fingers in our mouths 

 or touch our food with them ; we should cease 

 to ride in public conveyances, and, indeed, 

 should -cease to breathe common air. Absolute 

 prevention of the chance of infection is impos- 

 sible. The most that preventive medicine can 

 hope for is to point out the most common and 

 prolific sources of infection, and thus enable 

 civilized man to avoid some of his most common 

 troubles. It becomes a question, therefore, where 

 we will best draw the line in the employment of 

 safeguards. Shall we drink none except sterilized 

 milk, and no water unless boiled ? or shall we put 

 these occasional sources of danger in the same 

 category with bicycle and railroad accidents, dan- 

 gers which can be avoided by not using the bicycle 

 or riding on the rail, but in regard to which the 

 remedy is too oppressive for application ? 



Indeed, when viewed in a broad philosophical 

 light it may not be the best course for mankind 

 to shun all dangers. Strength in the organism 

 comes from the use rather than the disuse of our 

 powers. It is certain that the general health and 

 vigour of mankind is to be developed by meeting 

 rather than by shunning dangers. Resistance to 

 disease means bodily vigour, and this is to be de- 

 veloped in mankind by the application of the 

 principle of natural selection. In accordance 

 with this principle, disease will gradually remove 

 the individuals of weak resisting powers, leaving 

 those of greater vigour. Parasitic bacteria are 

 thus a means of preventing the continued life of 

 the weaker members of the community, and so 

 tend to strengthen mankind. By preventive med- 

 icine many a weak individual who would other- 



