178 PATHOGENIC BACTERIA. 



her cap placed over the cotton stopper, which is cut off 

 and pushed in, or by a rubber cork above the cotton, 

 the idea of this rubber corking being simply to prevent 

 evaporation. The tubes must be kept in an incubator 

 at the temperature of 37-38 C. 



Kitasato has published a method by which Koch has 

 been able to secure the tubercle bacillus in pure culture 

 from sputum. After carefully cleansing the mouth the 

 patient is allowed to expectorate into a sterile Petri dish. 

 By this method the contaminating bacteria from the 

 mouth and the receptacle are excluded, and the expecto- 

 rated material is made to contain only such bacteria as 

 were present in the lungs. The material is carefully 

 washed a great many times in renewed distilled sterile 

 water until all bacteria not enclosed in the muco-purulent 

 material are removed ; it is then carefully opened with 

 sterile instruments, and the culture-medium glycerin 

 agar-agar or blood-serum is inoculated from the centre. 

 Kitasato has been able by this method to demonstrate 

 that many of the bacilli ordinarily present in tubercular 

 sputum are dead, although they continue to stain well. 



In 1887, Nocard and Roux gave a great impetus to 

 investigations upon tuberculosis by their discovery that 

 the addition of 4-8 per cent, of glycerin to bouillon and 

 agar-agar would make them suitable for the development 

 of the bacillus, and that a much more luxuriant develop- 

 ment could be obtained upon these media than upon 

 blood-serum. The growth upon such "glycerin agar- 

 agar" much resembles that upon blood-serum (Fig. 56). 

 The growth upon bouillon with 4 per cent, of glycerin 

 is also luxuriant. As tubercle bacilli require considerable 

 oxygen for their proper development, they grow only 

 upon the surface of the bouillon, where a rather thick 

 mycoderma forms. The surface-growth is rather brittle, 

 and after a time gradually subsides fragment by fragment. 



The tubercle bacillus can be grown in gelatin to which 

 glycerin is added, but as its development only takes place 

 at 37-38 C., a temperature at which gelatin is always 



