1 1 6 THE INVOL UNTAR Y NER VO US S YSTEM 



intestine, are looked upon as due to a different cause from the 

 movements just considered, because they are preceded by inhibi- 

 tion and are put out of play by nicotine. Do such differences 

 necessarily imply the presence of a true reflex nervous system in 

 the intestine? 



I do not think that our present knowledge enables us to speak 

 positively on the subject. The main argument appears to be 

 based upon the evidence of a co-ordinated nervous activity in the 

 intestine, which shows itself by a purposeful inhibition of a part 

 of the intestine towards which the peristaltic wave is travelling. 

 This inhibition and the peristaltic contraction are both caused by 

 the presence of a bolus in the intestine or a pinch at any spot, 

 and are supposed to imply a true reflex activity in the myenteric 

 plexus. 



Now Bayliss and Starling, who discovered this law of the 

 intestine, showed in the same paper that the peristaltic wave was 

 not necessarily accompanied by a preceding relaxation of the 

 intestinal wall, for upon repetition of the experiment many times 

 in the same piece of gut, a most striking difference takes place 

 in this so-called reflex, in that the insertion of the bolus still 

 causes a contraction above the bolus but without any preceding 

 inhibition below the bolus. This contraction passes as a wave 

 of contraction down the intestine over the bolus without moving 

 it onwards appreciably, looking as though a strong movement of 

 the bolus was necessary for the causation of a preceding inhibi- 

 tion. So also, as pointed out by Cannon, a stimulation of the 

 gut may cause inhibition above and not below the point stimu- 

 lated. This has been observed by Bayliss and Starling, and 

 by Magnus in the isolated intestine. These observations sug- 

 gest that the inhibitory effect of a stimulus or a bolus is 

 not necessarily closely bound up in a purposeful manner with 

 a downward travelling peristaltic wave. It is possible to 

 look upon the effects produced as due to the stimulus affect- 

 ing two separate nervous arrangements, not necessarily closely 

 bound up together; by the stimulation of the one, a peri- 

 staltic wave of contraction is caused, by the stimulation of 

 the other, inhibition of some part of the gut is caused according 

 to the arrangement of the inhibitory nerves at the place stimu- 

 lated. It is striking, as Cannon observes, to see how variable is 



