128 HOUSEHOLD BACTERIOLOGY 



the body machine, which with sinister intent took pos- 

 session of our interiors and battled for our lives ; or 

 was a visitation of Providence about which we might 

 not inquire too curiously. Then suddenly we became 

 aware that the soil, air, and water, the surfaces of 

 plants and of our own bodies were swarming with 

 minute, invisible, living beings, some few of which 

 were of the greatest importance to man because they 

 were capable of inciting serious disorders. By a tech- 

 nical device of the laboratory it was soon found pos- 

 sible to secure these invisible plants from their various 

 sources, to separate them one from another, and to 

 cultivate and study them with as much precision as the 

 farmer grows and gathers his various crops. 



Of course at first the few harmful members of this 

 newly exploited group of living things cast a shadow 

 over all the rest. And we shuddered as the pioneer in 

 this new domain of science revealed the thousands 

 and tens of thousands of bacteria which we might be 

 swallowing with our glass of water or with our bunch 

 of grapes. But we were soon reassured, for we were 

 told that we had nothing to fear from the rank and 

 file of our humble, newly discovered commensals ; that, 

 on the contrary, they were our friends, without which, 

 indeed, the world of life could not long continue. It 

 was only the few which we must avoid if we would 

 steer clear of tuberculosis, pneumonia, diphtheria, ty- 

 phoid fever, cholera, and a dozen or so others of the 

 uncanny brood of infectious, diseases. 



