74 



MANUAL OF BACTERIOLOGY. 



or blood-semm, 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- 



JA 



Fig. 20. — Stab Culture. 

 A rubber stopper may be 



used to prevent drying, 



see page 79. 



Fig. 21. — 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 ex- 

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

 allowed to sputter in the flame. 



It must be remembered also that such organisms as moulds develop 

 spores which are formed on filaments elevated above the surface of the medium 

 and are easily detached. 



