v] METHODS OF INOCULATION 55 



loop in one, two, three or more lines along the slanting 

 surface of the solid medium, or rubbing it all over this 

 surface. 



If we have, however, a culture-fluid or any material that 

 contains, as the microscopical examination proves, various 

 species of organisms, which we wish to isolate, then the 

 method of Klebs of "fractional cultivation,'' or the method 

 of Lister and v. Nageli of " dilution," or better still, the 

 now universally-adopted method of Koch's "plate-culti- 

 vation," is resorted to. 



The " fractional cultivation " consists in the attempt to 

 isolate by successive cultivations the different organisms 

 that have been growing previously in the same culture. If 

 we take up by means of a capillary pipette or the point of a 

 platinum needle a trace of the culture-material, and inocu- 

 late with it in the manner above described a successive 

 series of new culture-tubes containing various nourishing 

 materials, and expose these tubes in the incubator to a definite 

 temperature, say 37" C, then the chances are that in the 

 first twelve or twenty-four hours not all the different species 

 of organisms sown out will have increased equally in num- 

 bers in all tubes ; most probably only one or two species in 

 each tube — i.e., the ones that grow best in this particular 

 medium and at this particular temperature — will be found to 

 have increased to an enormous extent, while the others have 

 made little or no progress as yet. The nourishing fluid 

 appears turbid, and filled chiefly with the one or two kinds 

 of organisms. Now take out with a fresh capillary pipette 

 or a platinum needle a minute droplet of this new culture 

 and inoculate with a trace of it a new culture-tube. The 

 chances are that you inoculate only one kind, that is, the 

 one which is most abundant or perhaps is solely present. 

 After twelve or twenty-four hours' incubation this new tube 



