666 GASTRO-INTESTINAL BACTERIOLOGY 
It must be remembered that while the greatest number of import- 
ant bacteria mentioned above occur at the levels indicate^, there is 
a mecha-nical transportatio,n of all intestinal bacteria from the higher 
to the lower levels, so that some organisms of all types are found in 
the dejecta. It is particularly important to realize that the types 
of bacteria outlined are those which can be identified by staining 
methods as numerically prominent at the various intestinal levels; 
these observations can be corroborated by appropriate cultural 
methods. Nevertheless, there is a wide disproportion between the 
numbers of each of the respective bacteria seen in stained preparations 
and the numbers of each type which develop in artificial media. Thus, 
Escherich^ observed that a preponderance of bacteria of normal nurs- 
lings' feces were Gram-positive bacilli, yet he never succeeded in grow- 
ing these bacilli in artificial media ; the principal types which developed 
in his cultures were B. coli and B. lactis aerogenes, organisms which 
are numerically in the minority in the intestines, but which grow lux- 
uriantly outside the body. It is now realized that he did not employ 
suitable conditions of culture to isolate the most prominent types of 
organisms. Undoubtedly much of the confusion which has attended 
the study of intestinal bacteriology in the past is attributable to the 
lack of appreciation of the cultural peculiarities of the intestinal 
organisms. 
Distribution of the Intestinal Flora of Artificially-fed Infants.— 
Escherich- directed attention to the striking dissimilarity between the 
intestinal flora of the breast-fed and the artificiall}--fed infant; cul- 
turally, morphologically and chemically the former is more homoge- 
neous than the latter. The most distinctive features of the dejecta 
of artificially-fed infants are: the relative increase of Gram-negative 
bacteria of the coli-aerogenes type, and of coccal forms of the Micro- 
coccus ovalis type, together with a diminution of B. bifidus. B. 
acidophilus is relatively more numerous, as a rule, in the artificially- 
fed infant than in the nursling. Proteolytic bacteria of several types 
are also of frequent occurrence,^ but they are not commonly found in 
the dejecta of normal nurslings. These organisms are frequently 
spore-forming bacilli, of which two principal groups are recognized- 
members of the aerobic group, of which B. mesentericus is a prominent 
type, and anaerobic bacteria; of the latter, B. aerogenes capsulatus is 
most widely known ; it frequently occurs in small numbers in the feces 
of artificially-fed infants.*^ The reaction of normal feces of artificially- 
fed babies is usually alkaline; culturally and chemically, the evidence 
of intestinal proteolysis of bacterial causation is more marked in these 
infants than in normal nurslings. 
The general distribution of types of bacteria at the different levels 
■ Loc. cit. - Loc. cit. ' Escherich: Loc. eit. 
* See Hibler (Untersuchungen iiber die pathogenen Anaeroben, Jena, 1908). Jungano 
and Distaso (Les Anaerobies, Paris, 1910), and Hall (Differentiation and Identification 
of the Sporulating Anaerobes, Jour. Infee. Dis., 1922, 30, 445. 
