CHAP, i.] TISSUES AND MECHANISMS OF DIGESTION. 495 



respiration is seriously interfered with, peristaltic movements 

 become very pronounced. Thus, in death by asphyxia or suffoca- 

 tion, an involuntary discharge of faeces, which is in part at least 

 the result of increased peristaltic action, is not an unfrequent 

 result ; and the marked peristaltic movements which are .so 

 frequently seen in an animal when the abdomen is laid open 

 immediately after death, appear to be due to the cessation of the 

 circulation and the consequent failure in the supply of blood to 

 the walls of the alimentary canal and not, as has been suggested, 

 to the contact with air of the peritoneal surface. Since it is 

 blood which brings oxygen to the tissues, failure in the supply of 

 blood is tantamount to failure in the supply of oxygen ; but the 

 blood current brings other things besides oxygen and also takes 

 things away ; and the failure of this action also probably, as well 

 as failure in the supply of oxygen, provokes the movements in 

 question. 



The movements thus produced are to some extent the result 

 of the deficient supply of blood acting directly on the walls of the 

 canal, though in asphyxia at all events this effect may be increased 

 by the too venous blood stimulating the central nervous system 

 and thus sending augmentor impulses down the vagus. 



With regard to the mode of action of the drugs which promote 

 peristaltic action it will be sufficient here to say that while some 

 such as nicotine appear to act directly on the walls of the canal, 

 others such as strychnia produce their effect chiefly by acting 

 through the central nervous system. 



