GASTRO-INTESriNAL FLORA OF NORMAL INFANTS ()(i<) 
rectum. It has been stated that at least 90 per cent of the bacteria 
of the feces are dead, or so attenuated in vitaHty that they are incapable 
of growing in artificial media. For various reasons the accuracy of 
this statement may be questioned, but there is little doubt that the 
nmnbers of viable bacteria in the relatively desiccated feces are less 
than those in the more fluid intestinal contents at the level of the cecum. 
The bacteria commonly present in the ileocecal region are undoubt- 
edly of many and varied types, but in general aerogenic bacilli of 
the colon type^ (including probably meml^ers of the proteus group as 
well) and aerobic spore-forming bacteria of the mesentericus group are 
the most readily recognized. The important feature of the intestinal 
flora at the lower levels of the intestinal tract of adolescents, and 
more especially of adults, is the presence of facultative-fermentative 
bacteria which appear to thrive equally well when the intestinal con- 
tents at this level contain protein and carbohydrate as when the 
carbohydrate is absent. Members of the colon-proteus group, par- 
ticularly the former, various aerobic liquefying bacilli— both spore- 
forming, and non-spore-forming— and, to a limited extent, anaerobic 
bacteria as well, are characteristic of the bacterial flora of the large 
intestines of adults. This is in striking contrast to the distinctive 
monotonous fermentative flora of the normal nursling, whose diet 
contains a sufficient amount of carbohydrate (lactose) to bathe the 
entire alimentary canal. It contrasts also, to a somewhat lesser degree, 
with the lower intestinal flora of young children on a cow's milk diet, 
where the proportion of carbohydrate to that of protein, although 
decidedly less than that of the nursling, is usually still sufficient to 
restrain an excessive development of proteolytic bacteria. 
It will be seen that the carbohydrate of the infant diet is lactose, 
which is utilizable as such by the dominant bacteria of the infantile 
intestinal and fecal flora. A not inconsiderable i)()rtion of the carbo- 
hydrate of the adult, on the contrary, is starch, which is not readily 
utilizable as such by a great majority of the intestinal or fecal l)acteria; 
it is very probable that a very considerable proportion of the assimil- 
able products of hydrolysis of the starch are absorbed rapidly from the 
intestinal contents and therefore there is normally but httle utilizable 
sugar available for the intestinal flora of adults. This is especially 
the case in the lower levels of the intestinal tract, where the stasis of 
the intestinal contents results in a differential accumulation of the 
more slowly hydrolyzed and absorbed protein. It would appear from 
these considerations that the relative absence of utilizable carbo- 
hydrate in the large intestine of adults would naturally be associated 
with a diminution of the obligate fermentative or carbohydrophihc 
organisms, and available evidence indicates that such is the case. 
' Ford (Classification and Distribution of the Intestinal Bacteria in Man, Studies from 
the Royal Victoria Hospital, 1903, 1, No. 5), and MacConkey (Jour. Hyg., 1905, 5, 333) 
have described the common types of aerobic bacilli in the intestinal tract. The cultural 
characters of the various aerogenic lactose-fermenting organisms, grouped for con- 
venience as the colon group, are clearly set forth in these monographs. 
