54 



PHARMACEUTICAL BACTERIOLOGY. 



may be, there is always a predominating type present, or, to state it more 

 correctly, it is the unusual development of the predominating type which 

 determines the diagnostic characteristics of the infection. 



It must also be borne in mind that bacteria behave differently when 

 taken out of their natural environment and placed in artificial culture media. 

 It does not at all follow that, in the case of a mixed infection, the predominat- 

 ing and diagnostic microbe will remain the predominating type when said 

 mixed infection is transferred to some artificial culture 

 medium. In fact, the predominating microbe may develop 

 very slowly or with great difficulty, if at all, in the artificial 

 culture media; whereas one or more of the associated 

 microbes may thrive remarkably well, soon entirely over- 

 shadowing the former. These and other conditions 

 occasion some of the great difficulties encountered in 

 determining the primary causes of some microbic and 

 protozoic diseases and infections. 



A. Test-tube Cultures.— Inoculate several test-tubes, 

 containing nutrient gelatin or agar gelatin, vnth any 



Fig. 30. Fig. 31. 



Fig. 30. — Cotton plugged tube with a potato slant resting on a bit of glass rod to 

 keep the potato out of the water in the bottom of the tube. {Williams.) 

 Fig. 31. — Manner of holding tubes when making subcultures. The cotton plugs, 

 removed from the two tubes, should be held in hand holding the platinum rod, as explained 

 in the text. (Williams.) 



material which is known to be bacterially infected. This is done by 

 touching the infected material with the tip of a, heat-sterilized (by 

 holding in flame of Bunsen burner until red hot) platinum needle (pre- 

 pared by fusing a platinum wire, i 1/2 inches long, into the end of a 

 glass rod, six to seven inches long), then removing the cotton plug from 

 the test-tube, and pushing the needle, carrying the microbes, into the culture 

 medium down to the very bottom of the tube. Replace the cotton plug at 

 once, pass the needle into the flame of the Bunsen burner until red hot, to 

 sterilize it, and lay aside for the next tube inoculation. This is known as a 

 deep stab tube inoculation. In this manner inoculate some five or six tubes. 



