STOMACH AND INTESTINE. 



353 



statement excludes the possibility of a net- 

 work, such as has been affirmed to exist by 

 Krause and others. Koelliker, in whose ad- 

 mirable work * the reader will find a copious 

 analysis of the latest observations on this 

 subject, sums them all up very impartially by 

 acknowledging, that, although he has never 

 been able to see a trace of such ramifications, 

 still he cannot venture altogether to deny their 

 existence. On the contrary, he thinks *it pos- 

 sible that the above simple mode of commence- 

 ment, which certainly holds good for the cy- 

 lindrical villi, ma) be exchanged, in the larger 

 of these processes, for one involving the pre- 

 sence of a greater number of lacteal canals, or 

 the absence of such blind extremities. 



But in conceding this much, Koelliker 

 points out what Valentin -f- seems previ- 

 ously to have suspected, the facility with 

 which a striated arrangement of the dark 

 fatty molecules within the chyliferous villus 

 may be mistaken for lacteal vessels. Nay 

 more, even the chyle of the central canal 

 sometimes separates by coagulation into striae, 

 which closely imitate a branched network. We 

 may add, that, in the various observations 

 which have been made on executed criminals, 

 the possibility of error has probably been in- 

 creased by the distended state of the vascular 

 and lacteal canals contained within the delicate 

 structure of the villus. 



Whatever be the case as regards these 

 conjectures, it seems to me that the large 

 simple tube, and the minute network, are far 

 too unlike to be regarded as mere degrees of 

 development of the same structure in differ- 

 ent villi. In like manner, the simple loop of 

 lacteal seen by Henle just beneath the base- 

 ment membrane is suspicious, not only from 

 its situation, but also from a fact noticed by 

 Valentin and Remak, that the central canal 

 sometimes coexists with it. And when we add 

 to the foregoing remarks, that the majority 

 of observers have been unable to see any 

 such ramifications, it will seem difficult to 

 avoid concluding, that each villus probably 

 contains a single large lacteal, which occu- 

 pies its centre, and ends by a blind extremity. 



The muscular constituent of the villus was 

 first discovered by Bruecke, and has since 

 been verified by Koelliker in many Birds and 

 Mammals. Its shape is that of a thin hollow 

 cone, which closely imitates the form of the 

 villus enclosing it. Hence, from whatever side 

 it is examined, it may be seen as a double lon- 

 gitudinal layer ; which is placed immediately 

 around both sides of the central lacteal ; and 

 lies so deeply within the villus, as to be beneath 

 its vessels, as well as much of its granular basis. 

 It is more distinct in the lower part of the 

 villus, and in the larger flat specimens ; but is 

 easily obscured by oil globules, nuclei, or pig- 

 ment. The nuclei of its fibre cells are best 

 seen on the addition of dilute acetic or nitric 

 acid, when they assume their ordinary charac- 

 teristic appearance. 



The action of this contractile apparatus 

 during life is at present unknown. Derived, 

 as it no doubt is, from that general expanse of 



Fig. 262. 



Supp. 



, cit. p. 1GO. et seq. 

 . cit. p. 684. 



VUlus denuded of epithelium, treated iciih acetic acid. 



From a young kitten. Magnified 350 diameters. 



(After Koelliker.) 



a, outline of the villus ; b, nuclei beneath this ; 

 c, nuclei of the unstriped muscle ; d, roundish nuclei 

 in the centre of the villus. 



unstriped muscular fibre which pervades the 

 whole mucous membrane of the alimentary 

 canal, one can hardly avoid ascribing to it a 

 function which is more or less similar, if not 

 indeed co-ordinate, with that of the general 

 stratum. That this function is in some respects 

 related to the static or passive mechanical cir- 

 cumstances of the mucous membrane, has 

 already been conjectured (p. 325.) in speaking 

 of the stomach. And the little we know of the 

 ordinary action of the analogous unstriped 

 element in the skin, rather confirms than con- 

 tradicts such a supposition. But its pecu- 

 liar position with respect to the end of the 

 lacteal trunk in the centre of the viilus, 

 to which it forms a kind of muscular and 

 contractile envelope has given rise to the 

 suspicion, that it effects the propulsion of 

 the chyle contained in this canal. 



How far such a process really obtains must 

 be determined by future research, which 

 ought especially to notice the precise con- 

 nection of this muscular stratum with that 

 of the mucous membrane generally. In the 

 meantime, we may notice that, as Koelliker 

 justly remarks, an active propulsion by these 

 longitudinal fibres would imply their alternate 

 contraction and relaxation.* But, assuming 



* He also adverts to their apparent want of 

 nerves, and to the essential independence of organic 

 muscle of all but mechanical irritations. However 



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