202 BACTERIOLOGY FOR NURSES 



of cross relationships, and in order to determine the subdivisions 

 and to differentiate the members of each subdivision careful 

 observation of their fermentative action on the various carbo- 

 hydrate media, and their agglutinative reaction in immune sera 

 is necessary. 



From the above it will be understood that around each par- 

 ticular type a number of variants are grouped. Thus, for example, 

 in different epidemics of dysentery different strains of bacilli 

 have been isolated, varying from each other only in minor details, 

 but corresponding in certain points which mark them as close 

 relatives and warrant their classification as one group. 



The Colon Group. The first description of a member of this 

 group was given by Emmerich in 1885, who isolated the organism 

 from the dejecta of a patient suffering from Asiatic cholera. In 

 1886 Escherich obtained a similar bacillus from the feces of healthy 

 infants, to which he gave the name Bacillus coli communis. Later 

 it was shown that closely allied types are normal inhabitants of 

 man and animals. 



The organisms are widely distributed in nature. Transferred 

 through the feces as manure or sewage, they are found on culti- 

 vated land and in surface waters. They are most abundant, 

 however, in the intestines of man and animals and particularly 

 in that portion from which they derive their name. Apart from 

 the fact that under certain conditions the organisms may excite 

 disease, they have special hygienic interest in that their presence 

 in water or milk is an indication of fecal pollution. The presence 

 of colon bacilli does not necessarily mean the presence of typhoid 

 or dysentery bacilli, but it indicates the possibility when the 

 contamination is of human origin. 



B. Coli Communis. The colon group contains many varieties ; 

 of these B. coli communis has probably been the most studied 

 and may be considered as the most representative. 



Morphology and Staining. The typical forms appear as 

 short rods with rounded ends ranging from 1 to 3 /* in length 

 and 0.4 to 0.7 /* in diameter. They possess seven or eight 

 peritrichic flagella. Motility, however, varies in the different 



