STOMACH AND INTESTINE. 



315 



tube. We should thus get two currents, 

 which, at least in situation, would be identical 

 with those produced by the peristalsis of the 

 succeeding interval. 



Action of the pylorus. The structure of the 

 pylorus (TTv\(opb y portce custos) has already 

 been described. As regards its action, it is 

 obviously the sphincter of the stomach. As 

 such, it has been supposed to possess a kind 

 of selective power ; by virtue of which it 

 contracts against the food in the earlier stage 

 of digestion, but subsequently relaxes to per- 

 mit the passage of the chyme. This view, 

 however, appears to me very doubtful. 



In the empty stomach, the pylorus is 

 generally open, and readily* allows of the 

 passage of bile from the duodenum. In the 

 early stage of digestion, it is firmly shut ; and 

 retains the contents of the organ against 

 gravity, or even against such a manual pressure 

 as readily expels them from the cardia. 



But just as in the second stage of gastric 

 digestion, it is plain that the valve does not 

 undergo any sudden or great relaxation, for 

 such would allow the passage of a large quan- 

 tity of the moving and semifluid food, much 

 of which would be still crude and undigested 

 so the very gradual diminution*!*, noticed by 

 Beaumont in the early stage, renders his in- 

 ference, that, even from the first, chyme 

 is constantly passing into the duodenum 

 very probably correct. J Supposing this to 

 be the case, it is evident that the action of 

 the pylorus must be very similar at both these 

 periods. And after numerous and careful 

 observations on this part of the Dog's stomach 

 towards the close of its digestive act, I have 

 never yet been able to substantiate any de- 

 finite relaxation of the pylorus ; or any but an 

 inconsiderable oozing of chyme at the time of 

 that active peristalsis which has been described 

 above. Hence I prefer to regard the passage 

 of the chyme as produced by that great increase 

 of force which the contractions of the pyloric 

 sac acquire at this period; a cause which 

 appears so sufficient, that it seems scarcely 

 justifiable to assume any additional one. The 

 supposed relaxation of the pylorus seems also 

 contradicted by a remark of Beaumont's, that, 

 even at the end of the process, when the 

 passage of chyme is greatly accelerated, the 

 above contractions still continue. 



In short, instead of a relaxed pylorus, 

 through which a moderate peristalsis urges 

 a selected portion of the food, it appears 



* Bile is almost always found in the empty 

 stomach of Dogs and Cats. (Compare Beaumont, 

 pp. 86, 87.) 



t The diminution due to absorption would pro- 

 bably be at first compensated by the addition of 

 gastric juice. 



| According to Magendie (Op. cit. p. 91.), the py- 

 lorus of the Horse is always found open, and is pro- 

 bably relaxed during life. It is only thus one can 

 explain the well-known fact, that the quantity of 

 food taken by this animal at an ordinary meal has 

 a bulk which amounts to four or five times that of 

 its distended stomach. Indeed, water has been 

 found in its caecum six minutes after being swal- 

 lowed. (Coleman in Abernethy's PhysiologiCiil 

 Lectures, p. 180.) 



the state of this aperture during the close of 

 gastric digestion is that of a contracted valve, 

 through which the tolerably uniform chyme 

 is being strained in small quantities, at fre- 

 quent intervals, by a comparatively violent 

 muscular contraction.* Hence the separa- 

 tion of the chyme from the other contents 

 of the stomach seems to be effected by a pro- 

 cess somewhat analogous to a coarse filtra- 

 tion, aided by pressure. 



How little the pylorus could reject the 

 " crude " portions of the tolerably homo- 

 geneous chyme, to transmit its more fluid or 

 dissolved constituents, is shown by the facility 

 with which indigestible substances of various 

 shapes and sizes pass into the duodenum. 

 Of these we can only say, that it is probable 

 they are generally carried through the con- 

 stricted pyloric sac and valve by a very forcible 

 peristalsis.f The weight and solidity of many 

 such masses allow them to remain some time 

 in the cardiac pouch, perhaps lodged behind 

 the transverse constriction which separates this 

 from the pyloric sac. Both of these circum- 

 stances often defer their passage to the later 

 stage of digestion. Smaller substances, how- 

 ever, sometimes traverse the whole canal in 

 so short J a space of time, that it is diffi- 

 cult to avoid believing that they leave the 

 stomach very shortly after entering it. 



But while we may thus regard the pyloric 

 valve as exerting but one and the same action 

 during the whole period of gastric digestion, 

 we shall find it difficult to substitute any 

 other theory of its action for that local 

 appreciation or selection which we have 

 attempted to refute. Its contraction is ac- 

 companied by that of the whole muscular coat 

 of the stomach ; of which the pylorus forms, 

 apparently, but a terminal thickening. And 

 of the only two other facts which are co- 

 temporaneous in their occurrence and dura- 

 tion viz., the presence of food, and of gastric 

 juice the first affords little explanation ; 

 while the second is more likely to be another 

 effect of the cause, whatever it may be, which 

 excites that co-ordinate muscular action in 

 which the pylorus appears to play an im- 

 portant, though simple, part. 



It is interesting to observe how little the 

 action of the pylorus is connected with any 

 stimulus other than a gastric one. The flow 

 of bile into the fasting stomach may perhaps 

 be regarded as a passage, such as this janitor 

 might well concede to a fluid which is not 

 only harmless, but recrementitious. But in 



* It is scarcely necessary to add, that the mecha- 

 nism of such an act does not require that the cardia 

 should be, however momentarily, the stronger valve 

 of the two. For the force of an obliterating peri- 

 stalsis would beat first almost spent upon the pylorus 

 towards which it sets. While that of a weaker con- 

 traction would be chiefly expended upon the py- 

 loric sac. And the residual force of both would 

 chiefly dilate the yielding and quiescent large ex- 

 tremity. 



t A peristalsis, the energy of which it is pro- 

 bable that they themselves increase. 



J Thus the author has known peas traverse the 

 canal in two hours. 



