304 TYPHOID FEVER. 



described in the method of isolation ; but on gelatine the 

 surface colonies are 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 char- 

 acteristic features. This film is loosely attached to the 

 surface, and can be easily scraped off. 



The growth on potatoes is most important. For several 

 days (at ordinary temperature) after inoculation there is 

 apparently no growth. If looked at obliquely, the surface 

 appears wet, and if the surface is scraped with the platinum 

 loop, a glistening track is left, and a cover-glass preparation 

 shows abundant growth. Later, however, a slight pellicle 

 with a dull, somewhat velvety surface, may appear, and this 

 may even assume a brown appearance. These characteristic 

 appearances are only seen when a fresh potato with an 

 acid reaction has been used. 



On bouillon incubated at 37 C. for twenty-four hours, 

 there is simply a uniform turbidity. Cover-glass preparations 

 made from such sometimes show filamentous forms of con- 

 siderable length, without apparent segmentation. 



Conditions of Groivth^ etc. The optimum temperature of 

 the typhoid bacillus is about 37 C., though it also flourishes 

 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 corre- 

 spond 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). 



The 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 intestines, it is relatively and abso- 

 lutely enormously increased in the latter situation, where it 



