170 THE STORY OF GERM LIFE. 



a foothold. After we learn that typhoid infec- 

 tious material must enter the mouth in order to 

 produce the disease; that tuberculosis may find 

 entrance through the nose in breathing, while 

 types of blood poisoning enter only through 

 wounds or broken skin, we learn at once funda- 

 mental facts as to the proper methods of meeting 

 these dangers. We learn that with some diseases 

 care exercised to prevent the swallowing of infec- 

 tious material is sufficient to prevent contagion, 

 while with others this is entirely insufficient. 

 When all these facts are understood it is almost 

 always perfectly possible to avoid contagion ; and 

 as these facts become more and more widely known 

 direct contagion is sure to become less frequent. 



Above all, it is telling us what becomes of the 

 pathogenic bacteria after being eliminated from 

 the body of the patient; how they may exist for 

 a long time still active ; how they may lurk in 

 filth or water dormant but alive, or how they may 

 even multiply there. Preventive medicine is tell- 

 ing us how to destroy those thus lying in wait for 

 a chance of infection, by discovering disinfect- 

 ants and telling us especially where and when to 

 use them. It has already taught us how to crush 

 out certain forms of epidemics by the proper 

 means of destroying bacteria, and is lessening 

 the dangers from contagious diseases. In short, 

 the study of bacteriology has brought us into a 

 condition where we are no longer helpless in the 

 presence of a raging epidemic. We no longer sit 

 in helpless dismay, as did our ancestors, when an 

 epidemic enters a community, but, knowing their 

 causes and sources, set about at once to remove 

 them. As a result, severe epidemics are becoming 

 comparatively short-lived. 



