78 



CLINICAL BACTERIOLOGY. 



naturally affords no protection against the thermophilic bac- 

 teria (p. 22). After sterilization has been effected, the ves- 

 sels and nutritive media must, as a matter of course, be 

 protected against all subsequent contamination, especially 

 through atmospheric germs. For this purpose the orifices 

 of the tubes are, even before they are filled, closed by means 

 of cotton stoppers ; the tubes are then sterilized by exposure 

 to dry heat at a temperature of 170 C. (338 F.), and the 

 fluid is introduced into them. The cotton filters the air, 

 and restrains the entrance of the germs. If molds find their 

 way upon the cotton stopper, they may, under certain cir- 

 cumstances, if the tubes have been kept for a long time, 

 penetrate the cotton with their mycelial filaments. This 

 undesirable occurrence is to be avoided by cutting off the 

 excess of cotton, exposing the free surface in the flame, and 



Fig. 12. i, A tube of blood-serum ; 2, a sterilized cotton swab in test-tube. 



then applying over it a closely fitting rubber cap that has 

 been previously disinfected in a I : 1000 solution of mercuric 

 chlorid. 



Preparation of Nutrient Media. Whereas, previously 

 to the time of Robert Koch, we were restricted almost ex- 

 clusively to the employment of fluid nutrient media, Koch, 

 through the addition of gelatinous substances that is, such 

 as become fluid when heated, and solid again when subse- 

 quently cooled introduced the use of solid, and at the 

 same time transparent, culture-media, which made it possi- 

 ble to isolate individual colonies of bacteria and to study 

 their development. 



The nutrient media that are most generally employed for 

 the cultivation of pathogenic bacteria are bouillon, gelatin, 

 agar-agar, blood-serum, and potato. 



(a) Preparation of Bouillon (Loffier). One pound of 

 chopped meat freed from fat and tendon is macerated for 



