SECTION IV. 
GASTROINTESTINAL BACTERIOLOGY. 
CHAPTER XXIX. 
GASTRO-IXTESTIXAL BACTERIOLOGY.i 
General Considerations.— x\n examination of the feces'- of a healthy 
adiih with the higher objectives of the microscope will show that a 
large portion of the fecal mass is made up of bacterial cells. An 
average-sized bacterial cell is very small indeed, measuring about 
1 micron in diameter and 2 microns in length, hence it is not surprising 
that various investigators have estimated the daily excretion of bac- 
teria by a healthy adult on a mixed diet at one hundred to thirty-three 
hundred billions. The bacteria when dried would weigh more than 
5 gm. and would contain about 0.6 gm. of nitrogen. A very consider- 
able proportion of the total nitrogen of the feces is contained in these 
bacteria. 
It is apparent that the ingested food does not contain this prodigious 
number of bacteria, consequently it must be assumed that there is 
a rapid development of the organisms in the intestinal tract. The 
theoretical progeny of a single bacterial cell of the more rapidly 
developing types may number millions in twenty-four hours, so that 
the mechanical possibility of a very great daily proliferation of bacteria 
is well established. It is obvious, therefore, that the alimentary canal, 
from the viewpoint of bacteriology, is a most efficient incubator and 
cultural medium combined, in which bacterial growth exceeds, both in 
intensity and complexity, that of any known medium. The range of 
reaction and composition of nutritive substances at different levels 
of the intestinal tract are such that theoretically a great variety of 
bacteria capable of developing at body temperature may find condi- 
tions favorable for their growth there. '^ The prominent types of 
bacteria that appear in the intestinal flora of a normal person are 
1 Kendall: Recent Advances in Intestinal Bacteriology, Am. Jour. Med. Hci., 1918, 
156, 157. 
2 Average weight 100 to 200 gm. per diem. 
3 Kendall: Jour. Biol. Chem., 1909, 6,499; Wisconsin Med. Jour., 191:^, 12, No. 1. 
