586 GASTRO-INTESTINAL BACTERIOLOGY 



can accommodate their metabolism to either a protein or carbo- 

 hydrate regimen become fermentative and produce lactic acid and 

 other products of the fermentation of carbohydrate in place of H 2 S and 

 NH 3 , indol, and other putrefactive products which characterize their 

 development in protein media 1 under these conditions. The obligately 

 proteolytic organisms tend to decrease in number because they are 

 unable to thrive in the presence of active fermentation, and the 

 carbohydrophilic bacteria increase both in numbers and in activity; 

 the type of carbohydrophilic organisms which develops depends upon 

 the carbohydrate fed and upon the length of time the diet is con- 

 tinued; Bacillus bifidus tends to increase in numbers 2 when-lactose is 

 the sugar, Bacillus acidophilus if maltose is substituted for lactose, 

 provided the regimen is maintained for several days. 3 



The changes in the intestinal flora from the bottle-fed infant to 

 adolescence and adult life depend somewhat upon the diet of the 

 individual. The general tendency in individuals on an average mixed 

 diet is for Bacillus coli to become the dominating organism; usually 

 about 75 per cent, of the viable bacteria of the feces are colon bacilli. 

 Of the remaining organisms, spore-forming organisms of the mesen- 

 tericus group are usually numerous, and gas bacilli may be found 

 relatively frequently, but in small numbers. Bacillus coli and Bacillus 

 mesentericus are among the most persistent of the intestinal bacteria 

 of adults. Those two organisms and no others were found in the 

 lower part of the large intestine of a man who abstained from all food 

 for thirty-one days. 4 The characteristic feature of the normal adult 

 fecal flora as compared with the infantile nursling flora is the very 

 heterogeneous variety of types of bacteria in the former, in sharp 

 contrast to the homogeneity of types of bacteria in the latter. 



Distribution of the Intestinal Flora in the Adolescent and Adult. 

 The stomach in health is quite free from bacteria as a rule. It has 

 been assumed in the past that the hydrochloric acidity may be a 

 factor in the destruction of organisms, but it should be remembered 

 that protein undergoing gastric digestion binds hydrochloric acid. 

 Nevertheless, bacterial activity is very limited in the stomach under 

 normal conditions. 



1 Kendall, Boston Med. and Surg. Jour., 1910, clxiii, 322; Pediatrics, 1910, xxii, No. 9. 



2 It is apparent that this change cannot take place unless there is a residuum of bifidi 

 in the intestinal tract to develop from. The same is true for Bacillus acidophilus. In 

 the absence of these types the dominant fermenting organisms will vary with the flora 

 of the individual. 



3 Kendall, Boston Med. and Surg. Jour., 1910, clxiii, 322. 



4 Kendall, Publication 203 of the Carnegie Institution of Washington. 1915, p. 232. 



