668 GASTRO-INTESTINAL BACTERIOLOGY 
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. B. coli and B. mesen- 
tericus 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.^ 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. 
The duodenum of adults is relatively poorly populated with bac- 
teria in interdigestive periods, and Cushing and Livingston- have 
called attention to the relative innocuousness of gunshot wounds at 
this level as contrasted with those at lower levels, where peritonitis 
practically invariably follows perforation of the gut. This phenomenon 
is not wholly attributable to the comparative paucity of bacteria in 
the duodenum as contrasted to lower levels; a final explanation is 
lacking at the present time. According to Gessner,^ staphylococci 
and streptococci are numerous in the duodenum, and Tavel and Lanz^ 
have made similar observations. More recent observations^ upon duo- 
denal contents obtained with the duodenal tube from adults have 
shown that the most common bacteria are Micrococcus ovalis (the 
Enterococcus) and members of the mucosus capsulatus group. A 
majority of the latter ferment starch vigorously. Breast-fed infants 
showed fewer bacteria in the duodenal region than did bottle-fed 
babies. 
The lower levels of the small intestines become progressively richer 
in bacteria. The relative slowness with which food passes through 
the intestines at the lower levels probably is a potent factor in creating 
conditions favorable for continual bacterial growth. As a rule cocci 
still predominate in the lower jejunum and upper ileum, but Gram- 
negative bacilli of the colon group appear in moderate numbers. 
The cecum and ascending colon are the regions of most intense bac- 
terial proliferation in health, but the number of living bacteria in the 
intestinal contents diminishes rather abruptly from the sigmoid to the 
' Kendall: Publication 203 of the Carnegie Institution of Washington, 1915, p. 232. 
2 Contributions to the Science of Medicine by the pupils of William Welch, 1900, 543. 
5 Arch. f. Hyg., 1889, 9, 128. 
■• Mitt. a. klin. d. Schweiz., vol. 1. 
'^ Kendall, Day, Walker and Haner: Jour. Infec. Dis., 1927, 40, (577. Goldman: 
Ibid., 1924, 34, 459. 
