ISOLATION OF MICEO-OEGAHISMS 



57 



microorganisms 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, SHOWING COLONIES OF VARIOUS FORMS. 



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 ah 

 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 



