THE RHYTHMIC AND PERISTALTIC MOVEMENTS 109 



Gaskell, has made a special study of this rhythmic vascular 

 system. In the leech there are two main longitudinal contractile 

 vessels situated absolutely laterally, which function as hearts ; 

 from these cross vessels arise in each segment which in addition 

 to supplying the body with blood connect the two lateral vessels 

 together. These connecting vessels, like the two lateral vessels, 

 are strongly contractile and like them are capable of independent 

 rhythmical contractions. Now the nerve cells in the leech are 

 very conspicuous and easily found wherever they are present. 

 My son has traced the nerve fibres from the central nervous 

 system to these blood vessels and never found a sign of a nerve 

 cell between them and the muscles of the blood vessels. Also 

 the regular rhythm of these lateral hearts continues after destruc- 

 tion of the central nervous system. The evidence seems to me 

 quite clear that the muscles of the vascular system in the leech 

 possess a normal rhythmical power entirely independent of the 

 presence of nerve cells. 



Finally we come to the consideration of the movements 

 of the alimentary canal. According to the investigations of 

 Kroriecker and Meltzer the peristaltic wave of contraction, 

 which passes along the oesophagus in the act of deglutition, is 

 of such a character that a bolus in the oesophagus causes con- 

 traction of the cesophageal muscle just above it, and relaxation 

 of the parts below. They attributed this law of peristalsis to the 

 action of the central nervous system chiefly because of Mosso's 

 observation that a peristaltic wave could be started at the upper 

 end of the oesophagus and travel to the stomach, even when the 

 oesophagus was completely cut through in its middle portion. 



Later Bayliss and Starling investigated the problem in the 

 intestine, and showed by means of the enterograph that here also, 

 when a peristaltic contraction was caused by stimulation at a spot, 

 the contraction commenced above the spot stimulated and was 

 accompanied by a relaxation of the intestine below the spot. 

 Further they showed that this ' law of the intestine ' held good 

 when all the nerves to the gut from the central nervous system 

 had been cut ; that, in fact, the mechanism, by which this co- 

 ordinated peristalsis was brought about, existed in the intestine 

 itself. They considered it to be nervous in nature, and that it 

 was in all probability situated in Auerbach's plexus. It has 

 been called the enteric nervous system. 



Later Magnus carried out a number of experiments on an 



