PLATE-CULTIVATIONS, 



another in the liquid state, as in the process of pre- 

 paring plate-cultures, or where a culture is made from 

 a tube in which the growth 

 has liquefied the gelatine, 

 it is obvious that the tubes 

 cannot be inverted, and they 

 must then be held and in- 

 oculated as in Fig. 28. To 

 inoculate those tubes of 

 nutrient agar-agar which 

 have been gelatinised ob- 

 liquely, the sterilised needle 

 with the material to be 

 cultivated is streaked over 

 the surface from below up- FIG. 27. 



METHOD OF INOCULATING 



wards. A TEST-TUBE CONTAINING 



STERILE NUTRIENT JELLY. 



PLATE-CULTIVATIONS. 



The key to the success of Koch's method of 

 cultivation on solid media consists in the employ- 

 ment of plate-cultivations. By this means, as 

 has already been mentioned (p. 60), a mixture of 

 bacteria, whether it be in fluids, excreta, or in 

 artificial cultivations, can be so treated that the 

 different species are isolated one from the other, 

 and perfectly pure cultivations established in 

 various nutrient media of each of the constituent 

 bacteria in the original mixture. We are enabled 



