1 1 8 THE INVOL UNTAR Y NER VO US S YSTEM 



reflex, for they state that as long as the contents of the proximal 

 colon are soft, a series of anti-peristaltic waves pass along it, 

 which are not preceded by inhibition ; as soon however as a 

 portion becomes hard a normal peristaltic wave occurs preceded 

 by inhibition and the hardened bolus is passed on to the distal 

 part of the colon. A true reflex necessitates at least sensory and 

 motor neurons in the intestine itself. At present we have no 

 evidence of the existence of sensory nerve cells in the gut, while 

 there is evidence that the sensory nerves of the gut arise from cells 

 in the posterior root ganglia. The very fact that nicotine will 

 prevent this reflex in the isolated gut, indicates that it is de- 

 pendent on the integrity of the synapse between a nerve fibre and 

 a nerve cell. The only nerve cells in the gut which are known 

 to have such a connexion are the vagus nerve cells, so that the 

 action of nicotine points in the direction that the reflex is due 

 to a direct stimulation of vagus fibres, i.e., of connector nerves 

 to the motor ganglia in the intestine. If, after the vagus 

 nerves have been cut and time allowed for degeneration, the 

 myenteric reflex becomes abolished, as the action of nicotine 

 indicates, then it seems to me we should have proof positive 

 that this so-called reflex is due simply to stimulation of vagus 

 fibres in the intestine. 



Although the investigation of the so-called myenteric reflex 

 after complete degeneration of all the vagal fibres to the small 

 intestine has not, as far as I know, been carried out, the corre- 

 sponding experiment for the large intestine is described in the 

 paper by Elliott and Barclay-Smith. The animal was a rat, 

 and the cord was completely destroyed below the ninth thor- 

 acic segment ; the muscles around the anal and vaginal orifices 

 quickly regained a high tone, and at the end of the sixth week 

 after the operation the colon was examined : " the disposition of 

 the contents was abnormal and suggestive of a sluggish intestine. 

 Though the rat had not been fed for the last twenty-four hours, 

 its caecum was full with material that extended into the lowest three 

 inches of the ileum, through the relaxed ileocolic sphincter. A 

 large soft mass occupied the proximal colon, where such would 

 assuredly never have been found in a normal animal : and the 

 hardening nodules in the distal colon were irregularly piled on 

 the top of one another. At no time were any movements seen 

 in the intermediate and distal colon. Antiperistalsis was once 



