THE CULTIVATION OF MICRO-ORGANISMS 1 05 



In using the Bunsen flame for sterilization, the innermost cone 

 near the base of the flame may be utilized for drying material on_ 

 the end of the wire. This inner cone is not burning and is com- 

 paratively cool, and after a little practice the end of the wire 

 is easily brought into it and dried without sputtering. Slowly 

 elevating the wire brings it gradually into hotter zones of the 

 flame until it glows. 



Bacteria do not of themselves leave a moist surface. They 

 are not even removed by moderate currents of air unless they 

 have been previously dried. Their distribution about the labora- 

 tory, therefore, results from relatively gross accidents or 

 gross carelessness. When material containing bacteria is acci- 

 dentally spilled, it should be covered at once with disinfectant 

 solution, such as i-iooo mercuric-chloride solution. As a rou- 

 tine procedure it is well to wash the work table daily with bi- 

 chloride solution and, when working with pathogenic bacteria, 

 to wash the hands at the end of the day's work, first with the 

 bichloride solution and then with soap and water. 



Isolation of Bacteria. In order to study any kind of bacteria 

 it is necessary to have the particular species separated from other 

 sorts with which it may be mixed. The earlier bacteriologists 

 endeavored to separate bacteria of different sorts by successive 

 transplantations through a series of tubes of fluid media, one 

 kind of bacteria outgrowing the rest. Isolation was also ac- 

 complished by diluting the material very highly and then in- 

 oculating one drop into each of a large number of tubes of 

 broth. Some tubes would thus receive no bacteria, others would 

 receive several, and occasionally one would receive only a single 

 germ and would give rise to a pure culture. Another early 

 method of separating a pathogenic species was by inoculation 

 of animals. The ability of the animal to prevent the development 

 of all but one species contained in the inoculated material was 

 utilized to obtain the first pure cultures of anthrax bacilli and 

 tubercle bacilli. These methods are successfully employed only 

 for relatively few bacterial species. 



