86 



MANUAL OF BACTERIOLOGY. 



When a tube of gelatin is to be inoculated the wire is 

 usually introduced into the medium vertically, " stab-cul- 

 ture " ; when a medium with a slanted surface is employed, 

 as agar, potato or blood-serum, the needle should lightly 

 streak the surface, "smear-culture" (Figs. 20 and 21). 



The safety and success of this method of inoculation de- 

 pend upon a principle which has been established by long 

 and repeated observation, namely, that bacteria do not of 

 themselves leave a moist surface. They should not, there- 



FIG. 20. 



FIG. 21. 



Stab-Culture. 



A rubber stopper may be 



used to prevent drying, 



see page 91. 



Smear-Culture. 



This tube shows the rubber 



cap used to prevent 



drying. 



fore, rise from the surface of the moist culture-medium, nor 

 drop from the needle during its transit, if proper care be 

 exercised. They may be thrown into the air if the needle 

 be allowed to sputter in the flame. 



