BACTERIAL METABOLISM WITHIN THE BODY 705 



from the standpoint of numbers a normal adult eliminates daily several 

 hundreds of billions of microorganisms in the feces. 



3. The opportunities for bacteria of the most varied kinds to enter 

 the mouth and to pass to the intestinal tract are almost unlimited. At 

 one time or another virtually all bacteria from the outside world may 

 thus become prospective tenants. Notwithstanding this possibility of a 

 most varied immigrant flora, the predominant and, presumably therefore, 

 the normal intestinal flora is composed of strikingly few types. The 

 daily proliferation of these few types is responsible for the bulk of bacteria 

 excreted in the feces. 



4. Starvation reduces the number of bacteria materially, but the 

 types found in the intestinal flora under such a condition are of the 

 normal kinds. 



5. A monotonous diet, in which carbohydrate continuously permeates 

 the intestinal tract, leads to a simplification of the intestinal flora. In 

 normal nurslings, obligately acidogenic bacteria of the bifidus type be- 

 come dominant. In dextrin-starch mediums, members of the Bacillus acid- 

 ophilus type predominate. 



6. The products characteristic of the activity of the obligate fer- 

 mentative flora are normally innocuous and in a measure protective, in that 

 the lactic acid generated is a deterrent to the growth of non-fermentative 

 [putrefactive] organisms. A similar phenomenon is observed in milk 

 soured outside the body. It does not ordinarily putrefy. 



7. It is sometimes observed that an overgrowth of acidogenic bac- 

 teria, as Bacillus acidophilus, may lead to intestinal disturbances, par- 

 ticularly in young children. An overgrowth of the gas bacillus [Bacillus 

 welchii] may also lead to, or be associated with, severe intestinal dis- 

 turbances which may become serious. 



8. Upon a diet in which the proportion of carbohydrate to protein is 

 nearly equal, leading to periods of ebb and flow of carbohydrate in the 

 lower levels of the intestinal tract, the facultative organisms, members of 

 the colon-proteus-mesentericus groups, become the principal kinds met 

 with. Such a flora is more varied because a greater number of bacteria 

 capable of deriving their energy from carbohydrate or protein can thrive 

 in the intestinal environment than appears to be possible with the more 

 or less obligately fermentative, lactic acid types. 



9. The facultative flora, in which periods of carbohydrate ebb and 

 flow is the dietary determinator, partakes of the acidogenic and amino- 

 tienic types respectively. At a given level of the tract, during these periods 

 in which ample carbohydrate is present, the acidogenic activities of the 

 flora are stimulated. During intervals of carbohydrate deficiency, the 

 proteolytic activities are resumed. 



10. A continuous, relative deficit of carbohydrate in proportion to 

 the protein in the diet leads to the establishment of a proteolytic flora, 



