CHAPTER XXV 



THE COLON-TYPHOID SEEIES OF BACTERIA 

 THE GENERA BACTERIUM AND PROTEUS 



This group of organisms is frequently termed the intes- 

 tinal group because many, although not all, of the organ- 

 isms belonging to it are of intestinal origin, or find the best 

 conditions for growth in the intestines of man or higher 

 animals and sometimes of birds or fishes. The group is im- 

 portant because belonging to it are several organisms 

 capable of causing disease in man and in animals, and 

 because the detection of certain bacteria belonging to it 

 constitute the most satisfactory method for the detection of 

 pollution in water. . 



The genera Bacterium and Proteus, that is, the organisms 

 belonging to the intestinal group of bacteria are rod-shaped. 

 Gram-negative, aerobic or facultative forms which do not 

 produce spores. Some species are motile, others nonmotile, 

 some produce capsules, others do not. Frequently there is 

 considerable power of fermentation of carbohydrates devel- 

 oped. 



The genera Bacterium and Proteus are very closely 

 related. The organisms belonging to the genus Proteus in 

 general liquefy gelatin more or less rapidly, while only a 

 few members of the genus Bacterium are capable of lique- 

 fying gelatin. These may be differentiated from members 

 of the genus Proteus by the fact that the latter are never 

 able to produce gas from the sugar lactose. 



The genus Bacterium is much more important than the 

 genus Proteus in the production of disease, and attention 

 will, therefore, be concentrated upon the former. Certain 



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