62 



PRINCIPLES OF BACTERIOLOGY 

 FIG. 44 FIG. 45 



fH) Ct 



H 



Two surface colonies of diphtheria bacilli upon agar. 

 X 500 diameters. 



FIG. 46 



Platinum needle, loop, 

 and spade. 



media as a rule will melt; 

 nor must the liquefying col- 

 onies be allowed to grow for 

 too long a time, or the entire 

 media will become fluid. 



Pure Cultures. If we 

 transfer without contamina- 

 tion bacteria from a colony 

 formed from a single organ- 

 ism to new media, and these 

 grow, we have what we call 

 a pure culture of that variety. 

 When these are transferred to the solid media we call the growth which 

 takes place from smearing the bacteria over the surface a surface or 

 smear culture, and that formed in the depth of the media by plunging 

 the needle carrying the bacteria into it a stab culture (Figs. 46 and 47). 

 In transferring bacteria from one tube to another we slant the tubes 

 so that no dust may fall within and contaminate with other bacteria 

 the special variety we wish to transplant. The greatest care must be 

 taken that the sterilized platinum needle used to transfer the bacteria 

 is not infected by touching any non-sterile matter. The upper rim 

 of culture tubes should be passed through the flame so as to destroy 

 any bacteria resting there. Even with our utmost care bacteria will 

 from time to time pass from the air or edges of our tubes into the culture 



Stab cultures of three cholera spirilla in gelatin, show- 

 ing in upper portion of growth considerable liquefaction 

 of nutrient gelatin. 



