74 CLINICAL BACTERIOLOGY. 



and in spite of their promptness in destroying bacteria in 

 test-tubes, they are not applicable to the living body, be- 

 cause they either fail or, employed in the necessary strength, 

 destroy not only the bacteria, but also the cells of the body. 

 The possibility, however, that a (disinfectant may yet be 

 found that will destroy only the bacteria without affecting 

 the tissues, must remain an open one. 



IV. METHODS OF CULTURE AND OF EXAMINA- 

 TION. 



STERILIZATION. 



In order to follow the individual varieties of bacteria 

 perfectly in the course of their development, and in order 

 to employ them in animal experimentation, ij; is necessary 

 to obtain them in pure culture. " In the making of such 

 pure cultures the most scrupulous care must be observed 

 to exclude the large number of bacteria that are every- 

 where present. The instruments employed in the various 

 manipulations, the nutrient media, and the vessels that 

 serve as the field of development for the bacteria, must be 

 absolutely germ-free sterile. To accomplish sterilization 

 of these, ordinary antiseptic measures can not be employed, 

 as the addition of substances capable of destroying the 

 germs or of inhibiting their activity would naturally render 

 the nutrient media unsuitable for culture-purposes. For 

 this reason heat exclusively is employed for the sterilization 

 of all materials used in the culture of bacteria, and both 

 dry heat, as well as moist heat, in the form- of live steam. 



Dry Heat. As dry heat penetrates but slowly into the 

 interior of objects, it is employed principally for the steril- 

 ization of articles of small volume only ; thus, platinum- 

 needles are sterilized directly by exposure to the flame of a 

 spirit-lamp or of a Bunsen burner, and other instruments 

 by being moved to and fro for about a minute immediately 

 above the flame. Articles made of glass and other sub- 

 stances that tolerate high temperatures are placed in a 

 double-walled sheet-iron receptacle covered with asbestos 

 (drying chamber), which is heated to between 150 C. 

 (302 F.) and ;/o C. (338 F.) by means of a gas-flame 

 burning beneath it. (Fig. 9.) After exposure for half an hour 

 to air thus heated to from 150 C. (302 F.) to 170 C. 



