99 



are not repesented in the figure, appear to be much shorter. 

 The distal intestine in both species is five or six times the 

 length of the rectum. No differences in physiological behaviour 

 were noted in the different species employed. 



Experimental Resui-ts. 

 Effects of Sodiiom and Calcium Salts. 



In my previous communication I pointed out that if the 

 preparation just described be laid upon a glass slide and wetted 

 with saline solution (m/8 NaCl) waves of peristalsis may be 

 seen passing along the intestine in the aboral direction. 

 Powerful contractions of the rectum and rectal glands are 

 usually evident, and may persist for some hours. If the pre- 

 paration be touched at about its middle with the point of a 

 camel hair brush soaked in pure m/8 calcium chloride solu- 

 tion, the peristalsis instantly ceases in the area so treated, but 

 the conduction of excitation is not inhibited. The wave of 

 peristalsis disappears on entering the treated region, reappear- 

 ing below it at the moment when it would have appeared had 

 the wave been normally propagated. Potassium chloride, in 

 like concentration, suppresses both contraction and conduction. 



In the present experiments I at first employed physio- 

 logical saline (m/8 NaCl) made up in tap-water, assuming 

 that the calcium and other salts present in the tap water would 

 provide a solution approximating more nearly to a ''physio- 

 logically balanced" mixture than pure sodium chloride. To 

 my surprise little or no movement was exhibited by the pre- 

 parations immersed in these solutions. Peristalsis of the distal 

 intestine was almost invariably absent, and a few twitches of 

 the rectal glands and incoordinate contractions of individual 

 fibres in the posterior rectum usually comprised all of the 

 movement observed. On placing a crystal of sodium chloride 

 in the drop of water containing the preparation, violent con- 

 tractions of the rectum and rectal glands took place. It was 

 inferred that the calcium chloride present in Adelaide tap 

 water was possibly sufficient to inhibit contractions, and that 

 its effect could be overcome by increasing the relative propor- 

 tion of sodium chloride, or, in other words, decreasing 



the -j;t— ratio to a favourable magnitude. I was subsequently 



informed by Dr.W. A. Hargreaves that the Adelaide tap water 

 contains about 0*058 grammes of calcium per litre, correspond- 

 ing, in am/8 solution of sodium chloride, to only one molecule 

 of calcium salt per 200 of sodium. Direct experiment showed 

 that a much higher proportion, about 1 to 12'5 of calcium to 

 sodium, is required to inhibit the movements of the intestine 

 in the manner and degree ill which they were inhibited by 



