THE METHODS OF CULTIVATING MICROBES 63 



inoculated with a mere trace of the original microbian 

 mixture, and are then placed in an incubator for a 

 couple of days or so. It will then be noticed that 

 the different species of microbes (sown in each tube) 

 will not have increased equally in numbers in all 

 the tubes (due, of course, to the nature of the 

 medium, the temperature, and the period of incuba- 

 tion). It is possible that only one species will have 

 developed, so far, in each tube. With these tubes 

 a similar number of tubes are re-inoculated, and so 

 on. By this fractional method of cultivation pure 

 growths are ultimately obtained. For further 

 information concerning this method the reader is 

 referred to Dr. Kleb's paper in the Archiv fur 

 Exper. Pathologic, 1873. 



The dilution method consists in greatly diluting a 

 drop of the original microbian mixture with some 

 sterile saline solution (0*5 / ). A series of tubes, 

 containing different cultivation media (sterilised), 

 are each inoculated, by means of a platinum needle 

 or glass pipette, with a mere trace of the diluted 

 mixture. After about thirty hours' incubation, 

 growths (most likely of one species only), make 

 their appearance in some of the tubes. The original 

 microbian mixture or fluid maybe diluted a thousand- 

 or even a million-fold, if the original fluid teems 

 with different microbes. The dilution method has 

 been largely used by Dr. P. Miquel in his examina- 

 tions of the different waters in and around Paris. 



By the fractional, dilution, and plate methods, 

 cultures containing many different species of 

 microbes are capable of being separated one from 



