344. 



STOMACH AND INTESTINE. 



the short intervals of this peristaltic act, the 

 irritation is incapable of exciting contraction. 



We may perhaps sum up all these re- 

 sults as follows. Direct irritation of this 

 mass of organic muscle excites loca con- 

 tractions ; which are of slower access, feebler 

 power, and longer duration, than those of the 

 striped fibre. Shortly after death, these con- 

 tractions of the intestinal coat evince a general 

 disposition to extend beyond the site of their 

 origin. But during life, this tendency is so 

 modified by some governing force, that, in obe- 

 dience to the requirements of the digestive 

 organ, it is either exalted into a definite and 

 effective peristalsis, or altogether suppressed. 

 This definite peristalsis forms the ordinary mus- 

 cular action of the bowel; and is the chief 

 agent in the proper propulsion of its contents. 

 As regards its intensity, we can only conjec- 

 ture that it is scarcely more than sufficient to 

 propel the normal contents. As respects its 

 character, it is essentially intermittent. As to 

 its extent, it seems to traverse long segments 

 of the tube. But it remains very doubtful 

 whether every or indeed any contraction 

 proceeds continuously throughout the whole 

 length of the intestine. Finally, we have a 

 right to suppose, that at least the more active 

 forms of peristalsis have in them so much of 

 rhythm, as to be not only repeated, but self- 

 repeating, at definite intermissions of time. 



But the exact mechanism of this peristalsis 

 remains in obscurity. Nay, more, the infor- 

 mation at present at our disposal will not even 

 enable us to take the first step in that process 

 of induction by which alone it will probably 

 be arrived at. 



In his admirable Essay on Muscular Move- 

 ment, E.Weber* haswellillustrated the peculiar 

 characters of the contractions which are ex- 

 cited by the irritation of organic muscle. He 

 has shown that in the Tench (Cyprinus tinea), 

 in whom the muscular coat of the intestine is 

 composed of striped or animal fibre, galvaniz- 

 ing the chief nerves of the tube produces an 

 immediate, powerful, and cotemporaneous con- 

 traction, in place of the slow, feeble, intermit- 

 tent, and enduring action seen in the unstriped 

 or organic intestinal muscle of the other Cy- 

 prinoid species. He has also found that the 

 Iris of various animals repeats the same con- 

 trast of structure and irritability. Hence he 

 argues, that the organic muscle is less directly 

 influenced by the nerves; and that these are 

 only connected with this contractile tissue in 

 some such mediate way, as that by which irri- 

 tation of the sensitive or afferent nerves gives 

 rise to the reflex movements which are pro- 

 ducible in voluntary or striped muscle. 



But do these facts warrant such a conclu- 

 sion ? On the contrary, do they not render 

 it more probable, that the above varieties of 

 contraction are in some way inherent to the 

 very structure in which these kindred animals 

 differ, rather than that they are brought about 

 by supposed differences of the nervous centres 

 or trunks : differences (.by the way) such as the 

 existing state of our knowledge would rather 



* Wagner's Handwoerterbuch der Physiologie. 



contradict than establish ? In the intestine of a 

 single Cyprinoid species, the fibre-cell gives 

 place to the striped fibre. Hence, failing all 

 proof of other differences, is it not precisely 

 to this remarkable contrast of structure, that 

 we must refer the parallel contrast which is 

 observed in its contraction, when a stimulus 

 is applied to its nerves ? 



This direct reference to the structure of 

 the organic muscle seems to be most justifi- 

 able in the case of the local contractions 

 above alluded to ; many of the peculiarities 

 of which are almost what might have been 

 expected from the rudimentary structure, the 

 little vascularity, and (especially) the mode of 

 aggregation, of the fibre- cells. But as re- 

 gards the less local contractions of the un- 

 striped fibre, their tendency to peristalsis and 

 intermission soon after death, appears to de- 

 mand some wider and less continuous connec- 

 tion of different points and times, than the 

 tissue itself would directly afford. Such a 

 means of association suggests itself in the ner- 

 vous system. And, since the removal of the 

 mesentery does not deprive the contractions 

 of this peristaltic character, any supposition 

 of this kind would appear to refer it to the 

 nerves within the walls of the intestine. But 

 it is difficult to believe that these nerves have 

 ganglia ; nor have any of these essential 

 elements of a nervous centre ever been seen 

 in this situation. While it has been pointed 

 out by Wild, that the excision of a portion of 

 the oesophagus prevents all propagation of its 

 peristalsis beyond the interrupted point: a 

 fact which tends to show that the contraction 

 of each segment is in some way conditionated 

 by that of its immediate predecessor. The 

 latter experiment, however, supposes such a 

 serious interference with the tube, that any 

 negative result can hardly be regarded as con- 

 clusive. And hence, until future researches 

 bring additional information respecting the 

 ultimate distribution of the nerves of this un- 

 striped muscular tunic, and the exact arrange- 

 ment of its constituent fibre-cells, the relative 

 share of the muscular and nervous tissues in 

 these peculiar contractions can hardly be con- 

 jectured. The stimuli by which we excite them 

 in our experiments are in reality far too rude, 

 diffuse, and uncertain in their application, to 

 afford much ground for a decided preference 

 of either muscle or nerve, as forming the chief 

 modulator of that contractility which is, no 

 doubt, essentially inherent to the sarcous sub- 

 stance itself. 



From the appearances noticed in the healthy 

 intestine soon after death, it may be doubted, 

 indeed, whether even this last phrase is quite 

 specific enough; whether we ought not to 

 regard* contraction itself (rather than an ab- 

 stract "contractility") as the inherent pro- 

 perty of the living organic muscle. In the 

 observations just mentioned, we have seen 

 that the death of the animal was soon fol- 

 lowed by an irregular, but distinct, contrac- 



* A contraction answering to what has been phi- 

 losophically distinguished by Professor Bowman as 

 "passive" in the case of the striped muscle. 



