MOVEMENTS OF STOMACH AND INTESTINE. 263 



from the cardiac orifice, and then to spread themselves peristaltically 

 along the walls of the stomach ; but no such movements can he excited 

 if the stomach be empty. On the other hand, there is distinct proof 

 that all the movements necessary to digestion may take place after the 

 section of that nerve ; although the first effect of the operation appears 

 to be to suspend them completely. It is probable that the movements 

 of the stomach are more regular and energetic in Herbivorous animals, 

 whose food is difficult of digestion, than they are in the Carnivora, 

 whose aliment is dissolved with comparative facility. 



460. From the time that the ingested matter enters the Intestinal 

 tube, it is propelled onwards by the peristaltic contractions of its mus- 

 cular coat ; which are excited, independently of all nervous influence, 

 by the contact of the aliment, or by that of the secretions mingled with 

 it in its passage along the canal. These last appear to have an impor- 

 tant effect ; for we find that, when the bile-duct is tied, so as to prevent 

 the bile from entering the intestine, constipation always occurs; whilst 

 an increase of the biliary and other secretions, consequent upon the 

 action of mercury or upon any other cause, produces an increased 

 peristaltic movement, and a more rapid discharge of the excrementitious 

 matter. During the passage of the alimentary matter along the small 

 intestine, as we shall see hereafter, a large proportion of its fluid is 

 removed, by the absorbent power of the villi ; and the residue is again 

 brought, therefore, to a more solid consistence. This residue consists 

 in part of those portions of the aliment, which are not ca'pable of being 

 dissolved or finely divided, so as to be received by the absorbents ; and 

 in part of the matters poured into the alimentary canal, by the various 

 glands that discharge their contents into it, for the purpose of being 

 carried out of the body. The faeces, which are thus formed, are pro- 

 pelled through the large intestine, by the continued peristaltic action 

 of its walls, until they arrive at the rectum. 



461. That the ordinary peristaltic action of the intestinal canal is 

 independent of nervous influence, is sufficiently indicated by the fact, 

 that it will continue when the tube is completely separated from all 

 connexion with the nervous sentres ; as well as by the difficulty, already 

 adverted to ( 353), of exciting contractions in the muscular coat by 

 any stimulation of its nerves. All the nerves of the intestine, fromjts 

 commencement at the pyloric orifice of the stomach to its termination 

 at the anus, are derived from the ganglia of the sympathetic system ; 

 but there is evidence that those which influen9e its movements are 

 really derived from the spinal cord (see CHAP, xn.) Although the will 

 has no influence whatever on the peristaltic movement, yet the emotions 

 seem to affect it ; and it is probably to convey their influence, that the 

 intestinal canal is supplied with motor nerves. It is also furnished with 

 sensory nerves, which form part of the trunks of the sympathetic 

 system, but which really pass onwards to the brain ; these do not, how- 

 ever, make us conscious of the passage of the alimentary matter along 

 the canal, so long as it is in a state of health ; but in various diseased 

 conditions, they give rise to sensations of the most painful nature. 



462. For the occasional discharge of the faeces from the rectum, and 

 for the retention of them at other times, we find the outlet or anal 



