372 



STOMACH AND INTESTINE. 



transition of the sigmoid flexure of the 

 colon into the rectum ; the second indicates 

 the spot where the bowel reaches the median 

 line of the sacrum ; and the first is nearly op- 

 posite to its bend in the hollow of the latter 

 bone and the coccyx. And frequent as their 

 presence undoubtedly is and important as 

 they therefore are with respect to the surgery 

 of the rectum, it may still be doubted 

 whether they possess those characteristic 

 anatomical features that would alone entitle 

 them to rank as true permanent folds, like the 

 transverse or falciform septa which isolate the 

 several pouches of the large intestine. For, 

 unlike these, they are not only somewhat irre- 

 gular in number and position, but are effaced 

 by complete distention of the tube. And, 

 finally, they appear to contain not a trace of 

 the proper transverse stratum of unstriped 

 fibres. Hence they probably exp/ess a mere 

 passive arrangement of the loose mucous 

 membrane; a relaxation which is perhaps 

 chiefly due to contraction of the powerful 

 longitudinal layer of the muscular coat of the 

 bowel. 



In the rectum, the muscular lamina of the 

 mucous membrane resumes its usual thick- 

 ness. At the lower part of the bowel, the 

 skin and mucous membrane become con- 

 tinuous with each other. But, as might be 

 expected from the great dissimilarity of these 

 structures, there is a distinct line of demarcation 

 between the two. Their junction is situate, 

 not exactly at the anus, but at a point from 

 two to four or five lines above this aperture. 

 Here the skin terminates by a wavy margin, 

 having a distant resemblance with that dentate 

 edge, by which the thick white epithelium of 

 the oesophagus adjoins the delicate pink mu- 

 cous membrane of the stomach. And the 

 apex of each of these waves usually corre- 

 sponds to the starting point of a longitudinal 

 fold of mucous membrane ; which, after pro- 

 ceeding a short distance up the bowel, either 

 becomes indistinct and disappears, or is crossed 

 and effaced by others that take a different 

 direction. It is nearly in this situation that 

 Kohlrausch * describes a thin layer of un- 

 striped muscular fibres, lying between the 

 sphincter ani internus and the mucous mem- 

 brane. Traced upwards from their intimate 

 union with the latter structure, these fibres 

 are seen to take a longitudinal course; and 

 to end, about one and a half inches above 

 the aperture of the anus, by joining the layer 

 of circular fibres immediately external to them. 

 Regarding these latter as their origin, it is 

 evident that their action would raise the mu- 

 cous membrane, and oppose its prolapse. 

 Hence they are described as forming a " sus- 

 tentator tuniccB mucosce" Below its junction 

 with the mucous membrane, the moist skin 

 possesses its ordinary structure. And around 

 the anus, it is occupied by numerous hair 

 bulbs ; as well as by sebaceous follicles, which 

 pour forth a large quantity of a peculiar odo- 

 rous secretion. 



The contents of the large intestine are of 

 * Loc. cit. 



two kinds. The first is a mass which, usually 

 of a semifluid consistence, ranges from the 

 state of a thin liquid to that of a hard friable 

 solid. This mass, when evacuated from the 

 rectum, constitutes the faeces, ordure, or ex- 

 crement. The second is an elastic or ga- 

 seous fluid, which occupies the intestine in 

 very variable amount, and unless its quantity 

 be excessive, is not necessarily or regularly 

 expelled at all. 



Fceces. It will be some clue to the compo- 

 sition of the faeces if we recollect, that the 

 large intestine so far resembles the small, as 

 to justify our inferring that it continues the 

 various metamorphoses which the contents 

 of the canal begin to undergo in its upper 

 segments. These metamorphoses are due, 

 partly to a spontaneous decomposition of 

 the alimentary substances themselves, partly 

 to changes set up by the various secretions 

 mixed with them. And they are accom- 

 panied by processes of absorption and se- 

 cretion, which may probably be regarded 

 as in some degree peculiar to this segment 

 of the tube. Of these two processes, that 

 of absorption seems chiefly destined to de- 

 prive the intestinal contents of their more 

 watery and soluble parts. While the act of 

 secretion pours forth fluids which, from their 

 proximity to the end of the bowel, may be 

 assumed to be, in great extent, excremen- 

 titious. The matters thus excreted may be 

 divided, histologically, into two chief con- 

 stituents : a structureless alkaline fluid 

 which is furnished by the tubes ; and a scaly 

 epithelium, which is a desquamation from the 

 mucous membrane of the rectum. 



But it would be wrong to suppose that 

 the whole of the processes which engage 

 the contents of the large intestine can be 

 comprehended in three such acts of meta- 

 morphosis, absorption, and secretion as those 

 just alluded to. On the contrary, each of 

 these three exerts its usual complex reaction 

 upon the other two. Thus the soluble re- 

 sults of metamorphosis undergo absorption, 

 as do also some of the substances secreted. 

 The fluids secreted into the bowel no doubt 

 modify the spontaneous changes which en- 

 gage its contents. And, finally, the slow 

 transit of these contents along the intestine 

 is accompanied by the precipitation of in- 

 soluble matters from the various secretions 

 of the upper segments of the canal, prior to 

 their expulsion from its lower orifice. 



It has indeed been alleged, that the ccecum 

 is the seat of a special metamorphosis, which 

 repeats, as it were, the process of gastric 

 digestion: that its mucous membrane pours 

 out an acid secretion, which is capable of dis- 

 solving certain constituents of the food pre- 

 paratory to their absorption. But a closer 

 examination dispels this view, and assigns to 

 this segment an humbler office, which is 

 closely analogous to that of the neighbouring 

 portions of the canal. Its tubes, which have 

 precisely the structure of those found else- 

 where, pour out an equally alkaline secretion. 

 Its infusion, whether acidulated or otherwise, 



