INFECTIONS OF THE DIGESTIVE TRACT 35 



contents were intensely blue, the color diminishing in 

 intensity toward B until at C the color had almost 

 disappeared and had entirely disappeared between C 

 and D. The contents of the intestine obtained from D 

 blued only when exposed to air. When boiled with 

 hydrochloric acid, water, and hydrogen peroxide, they 

 became intensely blue. The contents of the colon 

 (between E and F) were not blue under water, but be- 

 came blue very quickly when exposed to air. The 

 mucus adhering to the mucous membrane of the intes- 

 tinal tract behaved in general like the intestinal contents 

 as regards the color. This experiment indicates that 

 beyond the middle of the small intestine the conditions 

 become rapidly anaerobic or very nearly so, since the 

 reduction of methylene blue in this concentration could 

 not occur in the presence of the air. The main factors 

 in the reduction process are, of course, the bacteria, and 

 it is noteworthy that the reduction of the methylene 

 blue begins at just that level of the intestine in which 

 the bacteria begin to be numerous. There is probably 

 in these cases not merely a reduction of the methylene 

 blue, but decomposition of this salt, with the liberation 

 of hydrochloric acid and the production of the methylene 

 blue leucobase. This is indicated by the behavior of 

 the leuco-body with hydrochloric acid. 



THE BACTERIA OF THE HUMAN DIGESTIVE TRACT AT DIF- 

 FERENT AGES IN APPARENTLY HEALTHY INDIVIDUALS 



While it is true that at all periods of life the human 

 digestive tract is the seat of the life activities of myriads 



