INOCULATION OF CULTURE-MEDIA 79 



Streaked Surface Plating. The surface of the medium, 

 hardened in a Petri dish, is scratched by a needle containing 

 the inoculating material, three or more streaks being made 

 without obtaining fresh material, so that the growth along 

 the streak or scratches will represent varying amounts of 

 the substance to be tested. In removing the cotton plugs 

 from the sterile tubes to carry out the inoculation the plugs 

 should remain between the fingers in such a way that the 

 part which comes in contact with the mouth of the tube will 

 not touch anything (Fig. 23). 



It is well to pass the mouth of the tube and the cotton 

 plugs through a flame, scorching the latter before reinserting; 



Fig. 23. Manner of holding plugs. 



Sterilizing Needle. Sterilize needles by passing through 

 the flame before and after each inoculation; also sterilize the 

 glass part, as it is liable to become infected. 



After the needle has been withdrawn, the plugs are rein- 

 serted and the tubes labeled with the kind and date of culture. 



Plate Cultures. Several tubes of the culture-medium 

 are made liquid by heating in water-bath, and then inocu- 

 lated with the material as follows. A looped platinum needle 

 is dipped into the material and then shaken in the tube of 

 liquid media (gelatin, agar, etc.). 



This first tube is called original. From this three drops 

 (taken with the looped platinum rod, Fig. u, p. 45) are 

 placed in a second tube, the rod being shaken somewhat in the 



