PATHOGENIC BACTERIA. 105 



FIG. 55. FIG. 56. 



Typhoid fever bacillus in pure cul- Colonies of typhoid bacilli 3 days . 

 ture. 650 diameters. old 100 X- (Frankel and Pfeiffer.) 



Growth. They are facultative anaerobic ; grow best at 37 

 C., but can also develop at ordinary room temperature. All 

 nutrient media can be used as culture ground. They develop 

 chiefly on the surface, and very slowly. 



Colonies on Gelatine Plates. Two forms ; the ones near the 

 surface spread out like a leaf, transparent with bluish fluor- 

 escence. The deeper ones resemble whetstone crystals of uric 

 acid, the same yellowish tinge. 



In five days they attain to 3 millimetres in diameter. 



On Potato- Gelatine. The colonies do not have the yellow 

 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 48 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. 



Milk. They grow very well in milk without producing any 

 visible changes in its composition. 



Carbolized- Gelatine. Gelatine which has added to it y^ per 

 cent, carbolic acid will allow the typhoid bacillus to develop, 

 other similar bacilli being destroyed. 



