GAfiTEO-lNTESTINAL FLORA OF NORMAL INFANTS 007 
of the intestinal tract is similar to that observed in normal nnrslings; 
the principal difierences are fonnd in the cecnm and larj;'e intestine, 
where the obligately fermentative bacteria of the bifidus type are 
replaced to a considerable deijree by an extension of the habitat of 
the colon bacilkis, of B. acidophihis, and the ap])earance of moderate 
numbers of proteolytic bacteria, both aerobic and anaerobic; many of 
the latter are sporogenic. 
The prevailing bacteria of the artificially-fed infant may be changed 
along fairly definite lines by varying the proportion of protein to 
carbohydrate in the diet, and by substituting one carbohydrate for 
another. Thus, a continued preponderance of protein leads to a par- 
tial or even practically complete suppression of the activity of the 
bifidus-acidophilus group, and a noteworthy increase in the activity 
of proteolytic organisms;^ of the latter, aerogenic bacteria of the 
colon-proteus group and spore-forming bacteria of the mesentericus 
group appear to be the more prominent. A relative increase in carbo- 
hydrate leads to a diminution or suppression of proteolytic activity 
in the intestinal tract, and an increase in the fermentati\'e activities 
of the intestinal organisms." Those bacteria— as B. coli— which can 
accommodate their metabolism to either a protein or carbohydrate 
regimen become fermentative and produce lactic acid and other pro- 
ducts of the fermentation of carbohydrate in place of H>S and NH3, 
indol, and other putrefactive products which characterize their develop- 
ment in protein media-^ under these conditions. The obligately pro- 
teolytic organisms tend to decrease in number because they are unable 
to thrive in the presence of active fermentation, and the carbohy- 
drophilic bacteria increase both in numbers and in activity; the 
type of carbohydrophilic organisms which develop depends upon the 
car})ohydrate fed and upon the length of time the diet is continued; 
B. bifidus tends to increase in numbers^ when lactose is the sugar, B. 
acidophilus if maltose is substituted for lactose, provided the regimen 
is maintained for several days.^ 
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 B. coli to become the dominating organism; usually about 
75 per cent of the viable bacteria of the feces are colon l^acilli. Of 
1 Kendall: Jour. Biol. Chem., 1909, 6. 268. Herter and Kendall: Ibid., 1910, 7, 20.3. 
2 Provided, of course, the digestion of the infant remains normal. It is obvious that 
a disturbance of the digestive function of the alimentary canal may lead to new factors 
which may play an important part in determining the prevalence of one or several types 
of intestinal bacteria. 
3 Kendall: Boston Med. and Surg. Jour., 1910, 163, .322; Pediatrics, 1910, 22, No. 9. 
■• 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 of the dominant fermenting organi.sms the bacteria will vary 
with the flora of the individual. 
^ Kendall: Boston Med. and Surg. Jour., 1910, 163, 322. Rotch and Kendall: 
Am. Jour. Dis. Child., 1911, 2, 30. 
