G ASTRO-INTESTINAL FLORA OF NORMAL INFANTS 675 
group and those characteristic of the various bacteria which cause acute 
infections of intestinal origin are of unknown structure and complexity. 
The other prominent type of abnormal bacterial activity in the 
alimentary canal — the fermentative type — is of entirely different 
origin; the essential factor is either a decomposition of carbohydrates, 
with the formation of products abnormal for the intestine, or of excess 
of normal fermentative products. The abnormality may be a simple 
hyperacidity, as, for example, that caused by an overgrowth of aciduric 
bacteria when certain sugars, as maltose, fed in too large amounts, 
lead to an overdevelopment of the aciduric bacteria; or it may be 
Fig. 102. — Bacillus biilgaricus. (Photograph by Dr. J. H. Stcbbins, Jr., from the 
Fairchild culture of the Bacillus bulgaricus.) 
more complex. This happens frequently when there is an overgrowth 
of B. aerogenes capsulatus, or of members of the mucosus capsulatus 
group. In the latter event the exact nature of the irritative substance 
is as yet unknown. It is formed incidental to the fermentation of 
carbohydrates, which contain no nitrogen, but it may be histamine, or 
some physiologically similar substance.^ It may pass through the 
intestinal mucosa under definite conditions.- The factors leading to 
an overgrowth of these organisms in the intestinal tract a|)pear to be 
an excess of carbohydrate and a lack of normal lactic-acid-forming 
bacteria. It is a significant fact that diarrheal cases associated with an 
1 Kendall and Schmitt: Jour. Infec. Dis., 1920, 39, 250. 
2 Kendall and Varney: Ibid., 1927, 41, 143, 
