PATHOGENIC BACTERIA 



color, they are transparent; later on they become dark brown 

 with green iridescence. 



Stab-cultures. Mainly on the surface, a pearly layer. 



Stroke Cultures. A transparent thick layer. 



Potato. The growth here is quite characteristic. At 37 C. 

 in forty-eight hours a moist, transparent film is formed over 

 the whole surface, but so transparent that it can hardly be seen 

 without close observation. If a small portion of this is placed 

 under a microscope, it will be seen swarming with bacilli. 



The growth never becomes more prominent; the potato must 

 have a neutral or acid reaction. 



Fig. 67. Typhoid fever bacillus 

 in pure culture (x 650). 



Fig. 68. Colonies of typhoid 

 bacilli three days old (x 100) 

 (Friinkel and Pfeiffer). 



Milk. The bacteria grow very well in milk, producing a 

 slightly acid reaction, but no coagulation. 



Phenol Gelatin. Gelatin which has added to it -^ per cent, 

 phenol will allow the typhoid bacillus to develop, other similar 

 bacilli being destroyed. 



Glucose Gelatin. In glucose gelatin there is no gas-produc- 

 tion. Indol is likewise not generated by the typhoid bacillus, 

 whereas it is by the colon bacillus. On Eisner's potato-gelatin 

 the colon bacillus and the typhoid bacillus grow readily. The 

 medium of Hiss is of great assistance in isolating the germ. 



The Gruber-Widal blood-serum test, or, as it is otherwise 

 known, the agglutination phenomenon (Fig. 69), has the 

 following history: 



