324 TYPHOID FEVER 



rather more transparent than those on agar. Their characters, 

 as seen under a low power of the microscope, also correspond. 



In stroke cultures on agar there is a bluish-grey film of 

 growth, with fairly regular margins, but without any character- 

 istic features. This film is loosely attached to the surface, and 

 can be easily scraped off. 



The growth on potatoes is important. For several days (at 

 incubation temperature) after inoculation there is apparently 

 no growth. If looked at obliquely, the surface appears wet, 

 and if it is scraped with the platinum loop, a glistening track 



is left ; a cover-glass pre- 

 paration shows numerous 

 bacilli. Laterfhowever, 

 a slight pellicle with a 

 dull, somewhat velvety 

 surface may appear, and 

 this may even assume 

 a brown appearance) 

 These characteristic ap- 

 pearances are only seen 

 when a fresh potato with 

 an acid reaction has been 

 used. 



In bouillon incubated 

 at 37 C. for twenty-four 

 hours there is simply a 

 FIG. 114. Colonies of the typhoid bacillus uniform turbidity 

 (one superficial and three deep) in a gelatin Cover-glass preparations 

 plate. Three days growth at room tern- , ^ 



perature x 15. made from such some- 



times show filamentous 

 forms of considerable length without apparent segmentation. 



Conditions of Growth, etc. The optimum temperature of the 

 typhoid bacillus is about 37 C., though it also nourishes well at 

 the room temperature. It will not grow below 9 C. or above 

 42 C. Growth takes place in anaerobic as well as in aerobic 

 conditions. Its powers of resistance correspond with those of 

 most non-sporing bacteria. It is killed by exposure for half an 

 hour at 60 C., or for two or three minutes at 100 C. Typhoid 

 bacilli kept in distilled or in ordinary tap water have usually 

 been found to be dead after three weeks (Frankland). 



Bacillus coli communis. This bacillus is the chief organism 

 present in the small intestine in normal conditions, and, with 

 many other bacteria, it also inhabits the large intestine. During 

 typhoid fever, and other pathological conditions affecting the 



