HOW PARASITIC AND PATHOGENIC BACTERIA REACH MAN 103 
Oppler-Boas bacillus, sometimes called B. geniculatus,^ one of the 
aciduric bacteria, is so frequerltl^v found in this pathological condi- 
tion it was at one time supposed to be an accessory factor; it is now 
knowii to have no relationship to gastric carcinoma. B. geniculatus 
is also found very commonly in cases of achlorhydria. Sarcina ven- 
triculi- is also found in similar conditions. 
The gastric acidity will destroy the toxins of B. diphtheria? and 
B. tetani; the toxin of B. botulinus is not inacti\ated by the gastric 
juice.^ The toxins of the paratyphoid group of bacteria also appear 
to be resistant to gastric digestion. 
Intestines. — (See Chapter XXIX for details.) The abundant intes- 
tinal contents, which vary somewhat in composition and reaction at 
different levels, provide conditions which make the intestinal tract a 
very efficient combined incubator and culture medium. Many kinds 
of bacteria may theoretically find conditions well adapted to their rapid 
development there and it is not surprising to find that bacterial pro- 
liferation is greater both in nature and extent in the intestinal tract 
than in any other known medium. It has been conservatively esti- 
mated that the average daily fecal excretion of bacteria in a healthy 
adult on a normal diet is expressed by the truly enormous number, 
33 x 10^'. About 47 per cent of the nitrogen of the feces is contained 
in the bodies of these bacteria which, when dried, weigh nearly 0.5 gm. 
The upper level of the intestinal tract, particularly the fluodenum, 
is relatively free from bacteria during interdigestive periods. The 
duodenal bacterial population increases rapidly when food enters 
this section of the alimentary canal and decreases when the food 
passes to lower levels. The numbers of bacteria increase very greatly 
where stasis of food becomes more marked and in the cecum and large 
intestines generally there are continually present enormous numbers 
of bacteria.'' 
The types of bacteria found in the intestinal tract are influenced 
markedly by the nature of the food of the host and by the ability of 
the organisms themselves to change their metabolism to meet varia- 
tions in the composition of this food.^ Those bacteria which can best 
meet alternations in diet of the host are the ones which naturally 
persist. The bacteria contained in the food itself may also play a 
prominent part in determining the nature of the organisms which 
are found in the intestinal tract. The colon bacillus is particularly 
labile in meeting dietary alternations in the intestines and this organ- 
ism constitutes about 80 per cent of the bacteria which can be isolated 
from the feces of the adult. 
At birth the intestinal tract is sterile and the embryonal feces, the 
' Boas and Oppler: Deutsch. med. Wchnschr., 1895, 21, 73. 
2 Oppler: Sarcina ventriculi, Miinch. med. Wchnschr., 1894, 41, 570. 
' Dack: Jour. Infec. Dis., 1926, 38, 174. 
4 Kendall: Jour. Med. Res., 1911, 25, 117. 
6 Kendall: Am. Jour. Med. Sci., 1918, 156, 157. 
