TORSION OF THE DOUBLE COLON 251 



" antiperistaltic." Such a movement is considered abnormal, 

 but in the horse, according to Colin, antiperistalsis of the 

 small intestines is a natural condition. Some physiologists 

 recognize antiperistaltic movements of the large intestines as 

 being normal in certain animals, producing a to-and-fro move- 

 ment of the contents ; but it is generally thought that in the 

 small bowels antiperistalsis is only present under abnormal 

 circumstances. If antiperistalsis be admitted for the large 

 bowels, we see no difficulty in extending it to the small, 

 especially in view of CoUn's positive statement that it occurs. 

 The peristaltic wave depends upon a something peculiar to 

 the bowel wall, for if a piece of small intestine be experiment- 

 ally reversed, so that the portion originally nearest the stomach 

 is made to occupy a position farthest away from it, it is found 

 that the peristaltic wave in the reversed segment is still in the 

 original direction instead of in the new direction. The actual 

 mechanism involved in a peristaltic contraction, according to 

 Starling and Bayliss, is as follows : The circular muscle on the 

 stomach side of the bolus contracts, while that on the far side 

 is relaxed for some distance, so that the advancing wave drives 

 the bolus into a relaxed portion of the bowel. If a solution of 

 cocaine or nicotine be applied to the intestinal wall, these 

 movements cease, from which it is argued that they are prob- 

 ably due to local ganglia. 



'Rhythmical or fendular movements of the small intestines 

 were first described by Starling and Bayliss. They consist of 

 a series of local contractions caused by the presence of food in 

 the canal, and occur in the dog at the rate of about twelve a 

 minute, and in the cat thirty times a minute. They have been 

 studied by means of the Rontgen rays and a bismuth diet. 

 Pendular movements are essentially connected with the 

 division and subdivison of food in the intestinal canal. By 

 means of the rays, a string of material may be seen to become 

 suddenly segmented, each segment again dividing, and each 

 of these again, in a perfectly definite manner, may be further 

 subdivided. In this condition it is exposed to thorough 

 mixing with the secretions in the intestine, and to enable the 

 finely divided contents to be so acted upon, the bowel at the 

 time is free from peristalsis. When acted upon, a peristalsis 



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