DIGESTION 



229 



movements, and, as a matter of fact, we know that oxygen gas 

 normally does not exist, or only in traces, in the gaseous contents 

 of the bowels. Cutting 

 off the blood -supply 

 to the bowels causes 

 violent contractions, 

 which occur again 

 when the circulation 

 is re-established ; the 

 former is of interest 

 in those cases of twist 

 where the blood-supply 

 is wholly or partly in- 

 terfered with. 



Under normal con- 

 ditions the mind is not 

 conscious of peristaltic 

 movements, but when 

 these become very 

 energetic pain is pro- 

 duced. Under the in- 

 fluence of nervous 

 excitement rapid and 

 frequent evacuations 

 of the bowels may take 

 place in both cattle 

 and horses. So rapid 

 may the evacuations 

 be that in the horse, 

 in a short time, the 

 whole of the rectum 

 and single colon may 

 be unloaded. Ordi- 

 nary exercise is always 

 an important cause of 

 peristalsis, and of 

 keeping the posterior 

 bowels emptied. 



As previously re- 

 marked, the normal 

 stimulus to peristalsis 

 is the presence of in- 

 gesta in the canal. In 



Fig. 



81. — Abdominal Pre-Vertebral Sympa- 

 thetic System of the Horse. 



Anterior mesenteric ganglion ; 2, posterior 

 mesenteric ganglion ; 3, sympathetic cord 

 under the arches of the ribs ; 4, the splanchnic ; 

 & the vagus passing to the stomach ; 6, fibres 

 from the anterior mesenteric ganglion joining 

 the vagus ; 7. branches of the sympathetic 

 passing to the stomach ; 8, the stomach ; 

 9, the posterior aorta ; 10, the internal iliac 

 artery; n, the external iliac; 13, pelvic 

 branches of sympathetic ; 14, mesenteric 

 branches of sympathetic ; 15, the oesophagus ; 

 1 6, rich plexus formed by vagus and sympa- 

 thetic nerves. 



the feeding of herbi vora 

 bulk is essential, they cannot live in a state of health on concen- 

 trated food alone. Their intestines need bulk, if only in order to 



