CHAPTER XIX. 



THE COLON BACILLUS GROUP, PARACOLON, PARATYPHOID 

 DYSENTERY AND PARADYSENTERY BACILLI. 



The Colon Bacillus Group. 



THE first organism of this group was described by Emmerich (1885), 

 who obtained it from the blood, various organs, and intestinal dis- 

 charges of cholera patients at Naples. Similar organisms were after- 

 ward found by Escherich (1886) in the feces of healthy, milk-fed infants. 

 It has since been demonstrated that members of the colon group are 

 normal inhabitants of the intestines of man and of most of the lower 

 animals. 



Morphology. The bacillus coli varies considerably in its morphology, 

 according to the sources and the culture media from which it is 

 obtained. The typical form (Fig. 85) is that of short rods with 

 rounded ends, from OA/J. to 0.7// in diameter by 1, to 3, in length; 

 sometimes, especially where the culture media are not suitable for their 

 growth, the rods are so short as to be almost spherical, resembling 

 micrococci in appearance, and, again, they are somewhat oval in form 

 or are seen as threads of 6,u or more in length. The various forms 

 may often be associated in the same culture. The bacilli may occur 

 as single cells or as pairs joined end-to-end, rarely as short chains. 

 Capsules, though present, are not shown by the ordinary methods. 



FLAGELLA. Upon some varieties seven or eight flagella have been 

 demonstrated, upon others none. The flagella are shorter and more 

 delicate than those characteristic of the typhoid bacilli. There is 

 nothing in the morphology of this bacillus sufficiently characteristic for 

 its identification, for in this respect it simulates many other organisms. 



Staining. The colon bacillus stains readily with the ordinary aniline 

 colors; it is always decolorized by Gram's method. 



Biology. It is an aerobic, facultative anaerobic, non-liquefying bacil- 

 lus. It develops best at 37 C., but grows well at 20 C. and slowly at 

 10 C. It is usually motile, but the movements in some of the cultures 

 are so sluggish that a positive opinion is often difficult. In fresh cultures 

 frequently, only one or two individuals out of many show motility. 



Cultivation. The colon bacillus develops well on all the usual cul- 

 ture media. Its growth on them is usually more abundant than that 

 of the typhoid bacillus or the dysentery bacillus, but the difference 

 is not sufficient for a differential diagnosis. Although it grows best 

 aerobically, yet it grows well anaerobically, especially in media contain- 

 ing fermentable sugars. 



