488 



MUCOUS MEMBRANE. 



alcohol immediately on its removal from the 

 body ; a fragment of the tubes of Lieberkiihn 

 should then be scraped off, pulled to pieces, 

 and examined in a fluid medium under a 

 high power. The margins and rounded extre- 

 mities of the tubes will then be seen to be 

 sharply denned, as in the cases already men- 

 tioned, and to be formed by a structure inde- 

 pendent of the epithelium, which latter forms 

 !ths of their thickness. This structure is the 

 basement membrane. When masses of epithe- 

 lium, escaped from the tubes and bearing their 

 form, are met with floating around, their out- 

 line is uniformly irregular, and, as it were, 

 woolly. Sometimes, as in the kidney (Jig- 273), 

 the basement membrane is seen up to a certain 

 point only, beyond which it has been detached; 

 and in less recent specimens a tube of basement 

 membrane is sometimes seen, containing a mass 

 of broken-down epithelium. 



If the part selected for examination be the 

 stomach, the same precautions should be ob- 

 served, for here this membrane is, if possible, 

 more delicate than below the pylorus, and the 

 epithelial particles are often so large as to bulge 

 the tubes very irregularly, especially towards 

 their blind extremities. It is between these 

 bulges that the basement membrane may be 

 best seen (Jig. 276). 



Nothing' is more difficult than to explore, in 

 a satisfactory manner, the internal structure of 

 the intestinal villi. Their thick epithelial caps 

 and their abundant vascular rete are readily 

 demonstrable, but the arrangement of the lac- 

 teals, which undoubtedly exist in them, and 

 of the structure on which the epithelium imme- 

 diately rests, has hitherto almost entirely eluded 

 our research. In vertical sections of the recent 

 small intestine of the Car- 

 nivora, I have several times 

 seen the direct continuity 

 of the epithelium covering 

 the villi, with that lining the 

 tubes which open at their 

 base ; and also a distinct 

 continuity between the inte- 

 rior of the villi, where the 

 vessels are spread out, with 

 the vascular intervals be- 

 tween the tubes, which con- 

 tain the fine capillary web 

 surrounding the tubes, and 

 likewise give passage to the 

 branches to and from the 

 villi. It is then difficult to 

 avoid the belief that the 

 basement membrane of the 

 tubes is continued under the Lower extremity of a 

 epithelium of the Villi, to ^nach tubule from 

 , the dog ( Cants fa- 



support it, and form a part mUiarit^magntfied 

 of those remarkable projec- 300 diameters. 

 tions. Nevertheless 1 have 

 not been able to see it in an At a , the basement 

 . f membrane is seen 



isolated and distinct form, between b b b> 



and do not therefore assert bulging epithelial 



its positive existence ; only particles. 



I believe that the fact that 



the injected vessels of a villus, when seen in 



profile at its margin under u high power, and 



Fig. 276. 



when the epithelium has been removed, seldom 

 come to the extreme edge, is attributable to the 

 circumstance of the basement membrane still 

 investing them. This membrane, if it really 

 exist here, adheres intimately to the parts 

 within the villus. 



It might seem at first sight a hopeless task 

 to search in so dense and complicated a struc- 

 ture as the skin, for the analogue of a mem- 

 brane like that I have been describing, which, 

 in no situation where it can be unequivocally 

 brought into view, exceeds the 8000th of an 

 inch in thickness. But as it must exist, if at 

 all, between the epidermis and the vessels and 

 nerves of the cutis, in a position sufficiently 

 determinate, much of the apparent difficulty 

 is removed. The most favourable situations 

 for its detection are those in which the skin 

 is highly developed, presenting, like the small 

 intestine, villi (termed papillae) on its free sur- 

 face. The close resemblance between these 

 papillae and the villi of mucous membranes has 

 been observed by many anatomists. The dis- 

 tribution of the vessels within both is essentially 

 the same. Here, then, under the epidermic 

 layer, we might expect to find the basement 

 membrane. I have removed with great care 

 the whole of the epidermis from a thin ver- 

 tical section of such a specimen (and it is 

 better to have previously steeped it in solu- 

 tion of carbonate of potass), and have then 

 examined the outline of the bare papilla? with 

 a power of 300 diameters. This outline is 

 sharply defined, and appears to be formed 

 by a homogeneous membrane, enclosing the 

 vascular and nervous contents. This mem- 

 brane I believe to be that which I am now 

 describing, though, as in the case of the intes- 

 tinal villi, I have never been able to isolate it, 

 and thus unequivocally prove its presence. 

 This is a part of the skin which has never been 

 noticed by anatomists on account of its tenuity, 



Fig. 277. 



Qc, 



Part of the tubule of a sudoriferous gland from the 

 human axilla, muynijied 320 diameters, 



A, transverse section ; B, side view of the interior, 

 obtained by bringing the axis of the tubule into 

 focus ; a a a, basement membrane ; b b b, epi- 

 thelium ; c c, cavity of the tubule -, d, superficial 

 epithelial particles; e, deep epithelial particles ; 

 f, a detached superficial epithelial particle, 

 shewing the nucleus and pigmentary granules ; 

 i), its detached nucleus, with a nucleolus. 



