BACTERIA OF THE COLON TYPE IN HUMAN INTESTINES 247 



tion which will have permanent value. There is, however, some 

 justification in proposing a scheme of classification if it possesses 

 those elements of plausibility and suggestiveness which render 

 working hypotheses valuable assets in research. We now suggest 

 such a scheme which is based primarily upon a hypothesis pro- 

 posed in the first paper of this series (Rogers, Clark and Davis, 

 1914). 



The internal mechanism by which an organism converts its 

 food into energy and cell material is conceived to be more deep 

 seated and less variable than the processes by which a particular 

 substance is prepared for utilization. It is generally assumed 

 that substances like sucrose must be hydrolized before the con- 

 stituent glucose or fructose can be utilized. While definite evi- 

 dence of this is lacking we may assume it to be true. It is then 

 conceivable that since the inverting enzyme has only a prepara- 

 tory function it may be subject to some variation as the food 

 supply of the bacteria changes while the processes through which 

 the ultimate utilization of the carbohydrate is brought about 

 remain constant. The nature of the inverting enzymes is 

 shown by the particular polysaccharides utilized while the 

 processes which produce the final decomposition are indicated 

 by the end products of the fermentation. 



Such a conception assigns a position of secondary importance 

 to certain sugar fermentations and leads to a search for the sig- 

 nificant aspects in the ultimate metabolism. In the colon-aero- 

 genes group an indication of one special mechanism of fermenta- 

 tion is found in the varying amount and nature of the gases 

 produced. 



As previously suggested (Rogers, Clark and Davis, 1914) the 

 reaction by which carbon dioxid and hydrogen are liberated in 

 equal volumes may be common to the high and low ratio organ- 

 isms and the high gas ratio may result from an additional reac- 

 tion in which carbon dioxid alone is set free. It is suggestive 

 to note that we now have one group which produces equal 

 volumes of carbon dioxid and hydrogen, another which produces 

 an excess of carbon dioxid and a third which produces carbon 

 dioxid only and that all three groups appear to be generically 



