ISOLATION OF MICRO-ORGANISMS 



57 



micro-organisms and to identify them, and a further point 

 is that some microbes liquefy the solid gelatine, while 

 others leave its consistence unchanged (fig. 26) . 



The colonies of micro-organisms are best isolated in 

 the most diluted of the three cultures. 



If it is wished to obtain further cultivations from such 

 a plate, the following is the course adopted : A sample is 

 taken from a colony with the point of a platinum needle 

 fused into a glass rod (the needle being first sterilised at 



FIG. 26. GELATINE PLATE, 



COLONIES OP VAiimrs I--OU.MS 



red heat), or the whole colony is lifted on the point. In 

 either case a thrust is made into the sterilised gelatine in a 

 test-tube, or a streak is drawn over the oblique surface 

 of the solid agar-mass, or sterilised potatoes are infected. 

 Such a transference to different nutrient media enables 

 us to note all peculiarities in growth, and hence to gain an 

 inkling of the class in which the micro-organism under con- 

 sideration is to be included. This procedure is carried 

 out under a low power, and is designated * fishing.' It 



