266 APPLIED PHYSIOLOGY 



hand, and the contents of the bowel acquire a faecal 

 odour ; and the more watery the contents, the greater 

 is the degree of putrefaction. For this reason, if the 

 contents of the ileum be hurried into the colon very 

 rapidly and retained there, the stools may become very 

 offensive. This takes place in cases in which there is 

 catarrh limited to the small intestine. 



The gases of the intestine consist chiefly of nitrogen, 

 hydrogen, carbonic acid gas, sulphuretted hydrogen, and 

 marsh gas. Of these, the las.t four are produced by 

 bacterial action carbonic acid by fermentation of carbo- 

 hydrate in the small intestine ; H 2 S from proteins ; and 

 marsh gas and hydrogen from cellulose, and chiefly by 

 bacteria present in the colon. C0 2 is also produced by 

 the action of acids on the pancreatic and intestinal 

 juices. The possible source of nitrogen in the alimentary 

 canal has already been discussed. 



The gases of the intestine no doubt help to promote 

 peristalsis by their mechanical pressure on the wall of 

 the bowel, but sulphuretted hydrogen appears to act as a 

 7 chemical stimulant also. Sulphur apparently owes its 

 laxative properties to the production from it of H 2 S, 

 whilst the constipating action of bismuth may be due in 

 part to its power of fixing that gas. C0 2 seems also to 

 stimulate peristalsis when present in excess ; hence, 

 perhaps, the spontaneous action of the bowels which 

 sometimes occurs in asphyxia. 



Movements of the Colon. 



When the intestinal contents enter the colon a strong 

 general contraction takes place along the caecum and 



