248 L. A. ROGERS, W. M. CLARK AND H. A. LUBS 



related in so far as a general similarity in their morphology, 

 relation to external conditions and their metabolic activities 

 betokens such a relationship. 



Upon such a basis, which is of course hypothetical, there can be 

 constructed the provisional scheme of classification shown in 

 figure 5. This scheme recognizes in all members of the group an 

 ability to bring about some sort of fermentation of the simplest 

 carbohydrates. In what may be considered the lower members 

 of the group this fermentation is limited to the formation of 

 acids from simple sugars such as glucose. The four higher groups 

 beginning with B. enteritidis possess the ability to institute a 

 fermentation in which carbon dioxide and hydrogen are formed 

 in equal volumes. The B. aerogenes and B. cloacae groups are 

 differentiated still further by a secondary fermentation producing 

 additional carbon dioxide. With this is correlated the some- 

 what obscure carbinol reaction and in the case of B. cloacae 

 the secretion of proteolytic enzymes. The position of the so- 

 called B. proteus group in this diagram is questionable. We have 

 designated as B. proteus those organisms which produce no hy- 

 drogen. This is not compatible with the characteristics of 

 several cultures which others have furnished to us as B. proteus 

 but it is based on data obtained with some of these B. proteus 

 •cultures from other laboratories and on data obtained with seven 

 cultures in our collection from grain. All of these seven cultures 

 liquefied gelatin and six failed to ferment lactose. They would 

 ordinarily have been classed as J5. proteus, but whatever name is 

 used, such a group exists and is of relatively common occurrence. 



Inasmuch as all of our B. proteus cultures ferment sucrose 

 they have the general characteristics which would be possessed 

 by a B. cloacae culture in which the fermentation producing equal 

 volumes of carbon dioxide and hydrogen had been suppressed. 



This diagram, we believe, represents the probable evolution 

 from the highly organized B. cloacae group, amply qualified to 

 live an independent existence, to the parasitic pathogenic types. 

 This hypothesis is in accord with the reported distribution of the 

 different types. B. cloacae is common in soil and water while 

 B. aerogenes, its close relative, was found by us very commonly 



