STOMACH AND INTESTINE. 



367 



sistence of the faeces being such* as to mould 

 them to the cylindrical form of the last-named 

 portion of tube through which they have to 

 pass still it occurs so frequently in Man, and 

 so universally in many of those Herbivora in 

 whom we can best study the phenomena of a 

 highly developed large intestine, as to afford 

 a valuable testimony to the natural action 

 of this part. It is therefore difficult to avoid 

 believing, that the individual sacculi of the 

 colon, or at least of its later segments, retain 

 the faeces for a considerable period of time ; 

 during which they so far complete the action 

 of the large intestine upon these its contents, 

 as to leave nothing for its remaining segments 

 to effect, save their mechanical propulsion to- 

 wards the outlet of the canal. To this inter- 

 mittent action of the muscular coat in respect 

 of time, we may probably add a similar inter- 

 ruption as regards space. In other words, 

 the interrupted and irregular manner in which 

 the sacculi are often occupied by solid faeces, 

 entitles us to suspect, that different lengths of 

 the intestine can act independently of each 

 other. But it is difficult to hazard a con- 

 jecture as to whether the contraction of the 

 falciform transverse folds ever really shuts off 

 portions of the tube into distinct cavities. 

 The central axis of the figured evacuation is, 

 however, often so slender, or even interrupted, 

 as remarkably to corroborate such a view. 

 And some authors have assumed that the 

 caecum, during its digestive act, is isolated 

 from the ascending colon by a vigorous con- 

 traction of that large fold which is prolonged 

 from the frrena (or anterior and posterior 

 extremities) of the ilio-caecal valve.f 



The little information afforded us by direct 

 observation on the movements of the intestine, 

 confirms what is thus vaguely suggested by 

 the appearances of its expelled contents. The 

 highly developed large intestine of the living 

 or newly-killed rabbit, rarely exhibits any 

 noticeable movement whatever, when first ex- 

 posed to the air. By and bye, however, a kind 

 of irregular peristalsis comes on. But this is 

 nowhere quite so energetic as that seen under 

 similar circumstances in the small intestine ; 



* The consistence of even a figured evacuation is 

 sometimes so slight, as to render it highly probable, 

 that a general relaxation of that segment of in- 

 testine which originally contained the faecal mass 

 has accompanied the propulsive contraction of the 

 part immediately behind it. Such an apparently 

 co-ordinate relaxation of the muscular coat may be 

 frequently noticed in that vermicular movement 

 of the small intestine which is seen shortly after 

 death. An occurrence of this kind seems almost the 

 only way in which one can account for the fact, 

 that soft and semifluid faeces frequently retain the 

 form of the colon, after passing 'through its 

 falciform folds. Whether sucli an action is ever 

 effected by a contraction of the longitudinal bands 

 simultaneously with a relaxation of the circular or 

 falciform folds, it is impossible to determine. But 

 from their mechanism, and from the above appear- 

 ances of the faeces, it would seem more probable 

 that both these classes of fibres relax simultaneously. 



f Energetic contraction of the transverse fibres 

 of this valve would obviously aid in its occlusion ; 

 though we have already shown it to be probably 

 independent of all active muscular force. 



and is generally very feeble in the caecum.* 

 And in this movement, as in that produced 

 by mere local irritation, we may notice the 

 peculiar character before attributed to the 

 contraction of unstriped muscle generally ; 

 viz., that of diffusing itself over a time and 

 space greater than those occupied by the 

 irritation which has excited it. As regards 

 the details of this vermicular action, certain 

 sacculi contract and dilate alternately ; the 

 transverse constrictions between them shar- 

 ing in the same movement. This alternate 

 movement is often accompanied by an irregular 

 contraction of the longitudinal bands; which is 

 sometimes carried to such an extent, as to 

 shorten the tube, by approximating and di- 

 lating certain of its cells. And even where the 

 effect of the local irritation survives its cause, 

 so as to excite a continuous movement which 

 proceeds along a considerable length of intes- 

 tine, still it rarely affects all the cells of the 

 bowel exactly alike; but often passes lightly 

 over one or two, to bear with increased inten- 

 sity on those which immediately succeed them. 

 Very similar movements are produced by 

 galvanizing the solar plexus which gives off 

 the nerves to the large intestine. 



On the whole, therefore, the greater solidity 

 of the contents of the large intestine implies 

 a greater resistance to the contraction of its 

 muscular coat. And the structure of this 

 coat shows no proportionate increase, but 

 rather a decrease of strength. Hence we 

 might almost conjecture, that the general 

 movement of the small intestine is here ex- 

 changed for one which is slower, feebler, and 

 hence less effective : and which, besides being 

 much weaker, is possibly interrupted by 

 longer periods of rest.y 



But it is probable that this comparatively 

 feeble character of the general movement of 

 the large intestine is capable of being more 

 than compensated by that heightened efficacy 

 which the peculiar arrangement of its mus- 

 cular coat can concede. The thin muscular 

 stratum that forms the wall of its numerous 

 pouches, is evidently capable of assuming a 

 much smaller surface, in obedience to the 

 thick and powerful bands of its transverse 

 and longitudinal coats. Indeed, the simul- 

 taneous contraction of these two sets of 

 fibres would convert them into what would 

 form, for the time, a very thick and powerful 

 expanse of unstriped muscle, capable of ob- 

 literdting the entire calibre of the intestine. 



In this way the same muscular apparatus 



* The contractions by which this part responds 

 to a local stimulus are far more feeble, slow, and 

 uncertain, than those obtained in any other part of 

 the canal, the stomach not excepted. This character 

 seems to be a direct result of the tenuitv of the 

 muscular coat, which also attains its maximum here. 

 An incident which I have remarked in one or two 

 cases of intestinal obstruction appears to be partly 

 explained by the same structural peculiaritv. In 

 these instances, though the stricture was seated in 

 the descending colon, the dilatation and rupture 

 that formed the immediate cause of death occupied 

 the caecum. 



t Compare pp. 343, 344, 



