INFECTIONS OF THE DIGESTIVE TRACT 29 



air. Boycott * in his observations on the gases of the 

 intestine found that the small intestine of the cat gener- 

 ally contains a little oxygen, while the large intestine 

 holds either no oxygen or a smaller percentage than is 

 present in the small intestine. Sometimes the proportion 

 of oxygen in the gas from the large intestine was a little 

 above one part per hundred. Boycott noticed that oxy- 

 gen passes very readily out of the intestine, partly 

 by diffusion, but mainly by being appropriated by the 

 mucous membrane. There is apparently very little 

 direct exchange with the blood. In the stomach and 

 cavity of the mouth there is always a considerable 

 quantity of oxygen unless, indeed, the oxygen in the 

 stomach be displaced by the development of an abundance 

 of carbon dioxide, as sometimes happens. It is probably 

 safe to assume that in the mouth the free presence 

 of oxygen constantly acts as a deterrent to anaerobic 

 growth. In spite of this, however, anaerobic life is 

 possible, and the indications are accumulating which 

 point to the important part played by anaerobes in setting 

 up pathological states in the mouth. Caries of the teeth, 

 which was formerly referred to aerobic bacterial action, 

 seems clearly the result of the invasive action of anae- 

 robes on the tooth pulp. In certain derangements of 

 digestion, I have noticed that butyric acid fermentation 

 or putrefaction takes place with great rapidity in the 

 food particles that have lodged between the teeth, espe- 

 cially if carbohydrate food has been taken. It must be 



1 " Observations on the Gaseous Metabolism of the Small In- 

 testine of the Rabbit," Journ. of Physiol., xxxii, p. 343, 1904-05. 



