SECTION IV. 



GASTRO-INTESTINAL BACTERIOLOGY. 



CHAPTER XXX. 



GASTRO-INTESTINAL BACTERIOLOGY. 



General Considerations. An examination of the feces 1 of a healthy 

 adult 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 grams and would contain about 0.6 grams of nitrogen. A very 

 considerable 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. 2 The prominent types of 



1 Average weight 100 to 200 grams per diem. 



2 Kendall, Jour. Biol. Chem., 1909, vi, 499; Wisconsin Med. Jour., 1913, xii, No. 1. 



