116 



ESSENTIALS OF BACTERIOLOGY. 



nutrient media can be used as culture ground. They develop 

 chiefly on the surface, and very slowly. Repeated freezing and 

 thawing do not affect the vitality of the germ, and carbolic acid 

 in 1 to 2 per cent, solution has no effect on it. A ten-minute 

 exposure to 60 C. is invariably fatal. 



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, with 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. 



FIG. 59. 



FIG. 60. 



Typhoid fever bacillus in pure cul- 

 ture. 650 diameters. 



Colonies of typhoid hacilli 3 days 

 old 100 X- (Frankel and Pfeiffer.) 



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. The bacteria grow very well in milk, producing a 

 slightly acid reaction, but no coagulation. 



