THE COLON BACILLUS GROUP 



241 



rod form; relatively good growth on media; decolorization by Gram; 

 the lack of appreciable liquefaction of gelatin; the facultative properties; 

 indol formation; sugar fermentation; milk coagulation; motility; patho- 

 genic properties in animals to greater or less extent. The saprophytic 

 life of the colon bacillus leads to gradual variations according to con- 

 ditions. 



Association with Other Bacteria in the Intestines. In infant stools 

 we usually find in ordinary cultures only bacterium coli and bacterium 

 lactis aerogenes. Both fail to ferment albumin, and both markedly 

 ferment carbohydrates. The bacterium lactis aerogenes is most abundant 

 in the upper intestinal tract, the colon bacillus in the lower intestines. 

 The former appears to feed on the carbohydrates, the latter on sub- 

 stances secreted by the intestinal mucous membranes. Only about 

 10 per cent, of the bacteria seen under the microscope appear as colonies, 

 and whereas in infant stools the majority of the bacteria are frequently 

 Gram positive, the larger number of the colonies are composed of 

 Gram-negative bacteria. Some of the Gram-positive bacteria are 

 anaerobic; others fail to grow on ordinary culture media. These con- 

 ditions, the normal presence of colon bacilli and the tendency of other 

 bacteria not to grow in culture media, make the greatest care neces- 

 sary in weighing conclusions as to the pathogenic significance of colon 

 bacilli in disease. Further, although most colon bacilli seem alike in 

 the cruder methods formerly employed, it is now found that there are 

 many differences in their action upon carbohydrates and in their agglu- 

 tination affinities. There has thus come to be a group of colon bacilli 

 rather than a colon bacillus. Escherich restricts the name to bacilli 

 having the characteristics of those existing in the intestines of normal 

 nursing infants. 



The following schematic table illustrates some of the characteristics 

 of members of the colon group and of the typhoid bacilli : 



Bacilli of colon group 



Typhoid bacilli . . < . 



Motility. 



D 



E 



-f 



Lactose 

 fermen- 

 tation. 



Milk Indol \ Growth 



coagula- pro- Flagellaj on 

 tion . duction. potato. 



+ -f 



- 



Growth on 



Uchinsky 



media. 



The Colon Bacillus under Physiological and Pathological Conditions. 

 In the breast-fed infant within a few hours or days after birth one or two 

 varieties of typical colon bacilli are found in the colon, and these bacilli 

 form the great majority of all the bacteria present which grow in media. 

 The bacilli in one infant's intestines usually all agglutinate with the 

 same serum, but those from different infants vary. The bacilli find 



16 



