THE CULTIVATIOasr 03? MICRO-ORGANISMS 



109 



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 accidentally 

 spilled, it should be covered at once with disinfectant solution 

 such as i-iooo mercuric-chloride. solution. As a routine pro- 

 cedure it is well to wash the work table daily with bichloijde 

 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 tybes of fluid media, one 

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

 pUshed by diluting the material very highly and then inoculating 

 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 bac- 

 terial species. 



