226 A MANUAL OF VETERINARY PHYSIOLOGY 



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 sweeps together all the scattered atoms, and forms 

 them once more into a string of material. This remarkable 

 movement is unaffected by the action of cocaine or nicotine, 

 which have been shown to inhibit at once the ordinary peristaltic 

 movements. 



Besides peristaltic and pendular movements, another has been 

 described in the dog much slower, but also rhythmical, which may 

 be carried out for twenty or thirty minutes at intervals of two 

 hours, even when the canal is empty. 



We have been told by Colin that digestion in the small intes- 

 tines of the horse is carried on by peristalsis and antiperistalsis, 

 the fluid travelling from stomach to ileum, and from the ileum 

 towards the stomach. Pendular movements are of no value in 

 the small intestine of this animal, as the entire material, until the 

 ileum is reached, is fluid, so that there are no strings of food to 

 be segmented. This may account for pendular movements of 

 the bowels not having been observed in the horse. 



In the first and third portions of the colon of the horse the 

 ingesta travel by their own gravity ; in the second and fourth 

 portions they travel against gravity, as in the caecum. As the 

 first and fourth and second and third portions of the colon are 

 united, the curious results follow that material is passing along 

 each section apparently in two opposite directions. 



The frequency of intestinal affections in the horse causes the 

 canal to be of exceptional practical interest. When the caecum 

 is found completely inverted into the colon, as if a hand had 

 passed through the colo-caecal opening, laid hold of the apex of 

 the caecum, and drawn the entire bowel within the first portion of 

 the colon, it is then that the question of muscular movements so 

 strongly presents itself. Or, again, what is far commoner and 

 equally fatal — viz., displacement or actual twist of the large 

 bowel, or a complete twist of the small intestine, leaving the 

 bowels in such indescribable complexity that the parts cannot be 

 unravelled, even when removed from the body ! Finally, a 

 condition rare in the horse, probably in all animals, but still well 

 recognised, in which telescoping of the small bowels occurs, 

 known as ' intussusception.' It is impossible to believe that 

 muscular action of the intestines is free from all blame in the 

 production of these lesions. It is easier to understand a twist 

 of the small intestine apart from muscular action than it is to 

 understand displacement or actual twist of the large intestine. 



