BACTERIA OF THE COLON TYPE IN HUMAN INTESTINES 249 



on grains and in water but only occasionally in feces. B. coli, 

 on the other hand, is the principal organism found in the intes- 

 tines and does not thrive in natural conditions outside of the 

 animal body. All of the evidence available indicates that the 

 enteritidis, typhoid and dysenteric groups do not live normally 

 outside of the animal body. The proteus group is possibly an 

 offshoot of B. cloacae in which a part of the fermentative ability 

 has been lost. 



No biological species or genus has sharply defined limits and 

 it should not be assumed that the physiological characters are 

 restricted in the precise manner indicated in this diagram. It 

 is commonly assumed, for instance, that all members of the colon- 

 aerogenes group ferment lactose but it is very improbable that a 

 sharp distinction could be drawn in this way without excluding 

 cultures which by all other characters belong in this category. 

 While this distinction is habitually made in water bacteriology, 

 it is generally recognized that the exclusion of cultures, which, 

 while otherwise resembling colon, do not ferment lactose, is a 

 concession to the demand for rapid results justified by the fact 

 that it does not introduce a serious error. 



Clemesha (1912) speaks of a colon organism fermenting glucose 

 but not lactose as making up 4 or 5 per cent of the flora of the 

 intestines and says that lakes in India exposed for some time to 

 sunlight contained more of this type than any other. Our own 

 collection from human feces was made on the basis of fermentation 

 of lactose in conformity with the usual practice of American san- 

 itarians. It included, however, one culture which fermented 

 glucose but not lactose. This did not differ otherwise from the 

 typical low ratio culture. 



It may be argued that lactose is a unique carbohydrate in that 

 it is distinctly an animal sugar and that its fermentation or non- 

 fermentation is of more fundamental significance than the fer- 

 mentation of a distinctly plant sugar. We fail to see any logic 

 whatever in such an argument. It is comparable with con- 

 necting fermentability with optical rotation, neglecting the more 

 weighty matters of configuration and linkage within the sugar 

 group. It may be significant to note that of 177 cultures which 



