26 MICRO-ORGANISMS AND DISEASE. [CHAP. 



Quantity is required, it is carefully blown from the pipette, 

 f the sowing is to be carried out on the surface of the solid 

 nourishing material, the inoculation is of course performed by 

 depositing the seed on the surface ; if in the depth, the end 

 of the pipette is pushed down into the depth of the material 

 and the seed there deposited. The pipette is then altogether 

 withdrawn and the plug replaced as before. The new tube is 

 then placed in a beaker on a cushion of cotton-wool, and 

 exposed to the required temperature in the incubator. 



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

 tains, as the microscopical examination proves, various species 

 of organisms, which we wish to isolate, i.e. if we wish to 

 introduce into a new culture-tube only one species, then the 

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

 Lister and v. Nageli of " dilution," 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 a trace of the culture- 

 fluid, and inoculate with traces of it in the manner above 

 described a series of new culture-tubes containing various 

 nourishing materials, and expose these tubes in the incubator 

 to a definite temperature, say 35 C., then the chances are 

 that in the first twenty- four or thirty-six hours not all the 

 different species of organisms sown out will have increased 

 equally in numbers in all tubes ; most probably only one 

 species in each tube, i.e the one that grows 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 kind of 

 organism. Now draw out with a fresh capillary pipette 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 twenty-four hours' incubation 

 this new tube contains now probably only one kind of 

 organism. To make it quite certain, inoculate from this a 

 new culture-tube in the same manner, and now you probably 

 have sown only a single species. In this manner by continued 

 transference it is possible to obtain cultures with only one 

 species of organisms. Many conditions, such as naked-eye 

 appearances of a particular kind, coloration of the culture- 

 medium, formation of a pellicle, the quantity of growth in a 

 given time, soon indicate whether we have the desired b ingle 



