342 



STOMACH AND INTESTINE. 



extend backwards between them, so as to 

 shorten the length of its tether of mesentery. 

 The terms jejunum and ilcum refer to a 

 division of the small intestine which, though 

 to some extent an arbitrary one, is not only 

 too convenient to be altogether dispensed 

 \\ith, but is also connected with certain pecu- 

 liarities in the structure of the mucous mem- 

 brane, that will be hereafter alluded to. The 

 jejunum includes the upper two-fifths, and 

 the ileum the lower three-fifths, of the small 

 intestine.* 



Muscular coat. The muscular coat of the 

 small intestine consists of the fibre-cells pre- 

 viously described, the bundles of which are 

 arranged in two layers, an outer or longitu- 

 dinal, and an inner or circular. The first con- 

 stitutes a very delicate lamina, which is often 

 scarcely visible at the mesenteric border of 

 the tube, but is thickened at the opposite 

 margin, where it is firmly united to the perito- 

 neum. The circularfibres form a much stronger 

 and more perfect stratum ; and many of their 

 bundles, like those of the same layer in the 

 stomach, seem to take a slightly oblique di- 

 rection ; so as to join with others above and 

 below them. Both layers (and especially the 

 transverse) are somewhat stronger at their 

 commencement in the duodenum. But from 

 the middle of the jejunum their thickness 

 remains unaltered throughout the rest of 

 the small intestine. 



Movements of the intestine. The muscular 

 actions of the intestine have long been re- 

 duced to two: a normal peristalsis, which 

 urges the contents forwards towards the anus ; 

 and an abnormal antiperistalsis, by which they 

 are propelled backwards towards the stomach. 

 But each of these movements has rather been 

 maintained as adoctrine, than verified as a fact. 

 From the mere tenuity of the muscular 

 coat of the small intestine, we might infer 

 that its movements are much less vigorous 

 than those of the stomach and oesophagus, 

 in which this tunic has a thickness from two 

 to six times as great. Indeed, an active and 

 continuous peristalsis, like that which may be 

 seen in these segments of the canal, would 

 scarce allow the time necessary for the diges- 

 tive act. Even a slow progressive contrac- 

 tion of two inches per minute would traverse 

 the whole length of the intestine in from two 

 to three hours : a speed which we have 

 every reason to believe very unusual in the 

 healthy subject. 



To obtain direct evidence respecting these 

 movements, various methods have been re- 

 sorted to. 



In the healthy living intestine, it is but 

 very rarely that any definite muscular action 

 can be seen or felt through the wall of the 

 belly. In some of the Polyps, however, the 



* The former derives its name from the jejune 

 or empty state in which it is usually found after 

 death : and the latter either from its convoluted 

 form (eUe'w, circumvolvv'), its being the most fre- 

 quent seat of the disease called Hens, or its relation 

 to the iliac bone (on ilii). 



alimentary canal appears to exhibit a peri- 

 staltic, but intermittent, movement. And in 

 Man, the borborygmi which sometimes occur 

 in conditions but little removed from those 

 of health, constitute sufficient evidence of a 

 valid intestinal movement. While in cases in 

 which abnormal obstruction of the intestine 

 has been followed by an accumulation of fluid 

 in the segment above the occluded part, the 

 wall of the belly often becomes so extremely 

 distended and thinned, as to allow us to re- 

 cognise a progressive rolling contraction of 

 the dilated bowel. Such observations at least 

 prove that its muscular coat is capable of 

 very vigorous contraction, while in this state 

 of undue detention. 



When the intestines of a healthy living 

 animal are exposed by vivisections, surgical 

 operations, or accidental injuries, they are 

 found at rest. Hence, could we implicitly 

 trust these appearances, we should assign but 

 a very slight mechanical value to the intestinal 

 contractions. But such an estimate would 

 obviously be at variance with that propulsion 

 of their contents which we know them * to 

 effect. And, apart from this implied contradic- 

 tion, it is evident that such observations can 

 never be regarded as affording us trustworthy 

 evidence of what really obtains in the healthy 

 uninjured animal. For not only is it possible 

 that the slow and feeble contractions of the 

 intestine are much interfered with by the pain 

 and disturbance which such operations or 

 accidents presuppose, but I would add, that 

 there are considerable grounds for suspecting 

 that irritation of the peritoneal tunic of the 

 bowel can produce relaxation of its subjacent 

 muscular coat.-J- 



Until lately, it has been usual to augur the 

 movements which occur during life, from an 

 inspection of the intestines of healthy animals 

 immediately after their death. On laying 

 open the abdomen of a newly-killed animal, 

 its intestines are seen lying perfectly still. 

 But in a short time, those parts of them which 

 are exposed to the air begin to experience 

 vigorous contractile movements. In many 

 instances, these contractions are irregular and 

 undefinable, and are hence rather "vermicular" 

 than " peristaltic." But in other cases, they 

 take on appearances of a forward or backward 

 course, or sometimes of each of these direc- 

 tions alternately. Where transverse constric- 

 tion is marked, it almost always takes a di- 

 rection downwards, or towards the anus; and 

 is preceded by a dilatation which stretches 

 the intestine to the full length of its mesen- 

 tery. After a few minutes, the contraction of 



* It can scarcely be necessary to argue the ques- 

 tion which has sometimes been raised: namely, 

 whether it is the muscular wall of the belly, or the 

 muscular coat of the intestine, that propels the con- 

 tents of this tube. For this is obviously an inquirv, 

 which might be decided by a reference to its human 

 and comparative anatomy, even in the absence of all 

 direct observations as to the nature of its contrac- 

 tions, and their necessary mechanical effects. 



f The effect of scratching the peritoneal coat 

 (see opposite page) is perhaps partly due to an 

 action of this kind. 



