THE PHYSIOLOGY OF THE INTESTINES. 237 



vessels and nerves : the lacteals and numerous globate 

 glands are also situated within these membranous folds. 

 The origin of these folds of peritoneum is from the spme, 

 and is of small extent ; but it is so fi-amed, that, as it pro- 

 ceeds, it expands, and is enabled to follow the whole of the 

 intestines through their course ; branching out like a fan, 

 from its small beginning at the duodenum to its ample 

 termination at the small intestines. 



THE PHYSIOLOGY OF THE INTESTINES AND SOME OF THE 



VISCERA. 



The intestinal canal receives the pulpy mass of the chyme 

 in a partial state of digestion ; but this becoming mixed in 

 the duodenum with the pancreatic and the biUary fluids ; 

 further changes take place in it : chyhfication is by these 

 accessions more perfectly advanced, and the chyle more 

 completely animalized. The mass is continually propelled 

 onward by the creeping muscular contractions of the intes- 

 tinal tract, called their peristaltic motion. This motion is 

 not altogether uniform, either in direction or duration ; on 

 the contrary, it sometimes acts inversely ; occasionally it 

 halts altogether, and often is irregularly agitated. That 

 this propelling force may not huriy the contents too fast, a 

 cellular arrangement exists, evidently intended to delay the 

 chylous mass within the intestines till the whole of its nutri- 

 tive parts are taken up. The powers of the horse requiring 

 a very complete chyhfication, he is furnished with a long 

 and large alimentary tract. The chyle is separated from 

 the mass by the agency of the lacteals ; which vessels 

 directing their course through the mesentery, deposit their 

 contents in the chylous receptacle, by which it is conveyed 

 to the jugular or axillary vein, and mingled with the blood. 

 The intestines own a high degree of irritability, which in 

 their natural state produces vital phenomena ; and in their 

 deranged state causes some of the most fatal diseases. The 

 stimuli of the intestines are various ; food is the most ordi- 

 nary, and it is generally supposed to have its activity in- 

 creased by the biliary secretion. Exercise is also a natural 

 stimulus. The apphcation of particular substances u'ritates 

 them greatly, and are thence called purges. 



