18 BACTERIOLOGY FOR NURSES 



where; wherever air and dust find their way bacteria 

 are present. In the minutest crevices, too small to 

 be seen with the naked eye, like those in the skin, 

 upon the hair, upon all fabrics, furniture, walls, 

 floors, plants ; in the earth, water, and food they may 

 be found ; in fact, we may truthfully say they are 

 everywhere. 



The first and probably the greatest difficulty which 

 beset the early investigators was the presence of num- 

 berless kinds together, which effectually prevented 

 any opportunity to isolate a single species for obser- 

 vation. It was early discovered that bacteria would 

 grow in groups (colonies) which were sometimes 

 visible to the naked eye, but the microscope would 

 reveal not one species which might be studied, but 

 a dozen or more, and thus for years scientists labored 

 to devise some method whereby they might isolate 

 a single kind and study its habits. 



Bacteria were first grown artificially in bouillon 

 (beef broth), which was called the culture medium, 

 but the multiplicity of species and the fluid medium 

 were serious obstacles which blocked the way of sys- 

 tematic observation, and not until Robert Koch 

 found that gelatin was not unfavorable to bacterial 

 growth, and would solidify the broth, besides being 

 transparent, was it possible for pure cultures to be 



