NUTRIENT MEDIA AND METHODS OF CULTIVATION. 115 



Inoculation of the Tubes. A small portion of a culture or of the 

 material to be inoculated is taken up with a sterilised platinum 

 needle, and traced over the sloping surface of the serum ; or a 

 fragment of tissue, such as diphtheritic membrane or tubercle, may 

 be introduced into the tube and rubbed gently over the serum so as 

 not to break the surface. 



FIG. 44. HUEPPE'S SERUM INSPISSATOR. 



(D) PREPARATION AND EMPLOYMENT OF STERILISED POTATO. 



Potato-cultivations. Sterilised potatoes form an excellent 

 medium for the cultivation of many micro-organisms, more especially 

 the chromogenic species. Potato -cultivations also give in some cases 

 very characteristic appearances, which are of value in distinguishing 

 bacteria which possess morphological resemblances. 



Preparation of Sterilised Potatoes. Potatoes, preferably smooth - 

 skinned, which are free from "eyes" and rotten spots, should be 

 selected. If they cannot be obtained without eyes and spots, these 

 must be carefully picked out with the point of a knife. The potatoes 

 are well scrubbed with a stiff brush, and allowed to soak in 1 in 20 

 carbolic for a few minutes. They are then transferred to the potato- 



