Date of Award

Spring 1944

Document Type



Life & Environmental Sciences


The lower region of the mammalian intestinal tract presents almost ideal conditions for the growth of a diversity of microorganisms. Indeed, investigations carried on by various research workers on experimental animals and on man have shown that the intestinal tract of each animal under investigation possessed a characteristic and varied flora which remained fairly constant as long as there was no gross dietary deviation. Investigations carried out by J.R. Porter and L.F. Rettger at Yale University have shown that the characteristic flora of the intestinal tract of the rat can be altered somewhat by certain foods or by starvation, but that it is fairly stable despite the nature of the diet.

That the intestinal tract of the mammal should contain a varied and abundant flora of microorganisms is not remarkable. Indeed, the environment provided by the lower portion of the digestive tract is almost ideal for the growth of minute plant life--so ideal that many have regarded this lower region as a giant test tube. The partially decomposed food found here, which is both of a protein and of a carbohydrate nature, can be easily assimilated by the microorganisms; the temperature of the mammalian body (37.5 C) is optimum for the growth of a large number of organisms; the osmotic pressure requirement for the growth of minute life is satisfied by the moisture which is omnipresent even in the lower regions of the digestive tract; the acidic secretions of the upper digestive tract present an inhibitory action on the growth of organisms, but the lower tract has a pH which is not unfavorable for such growth.