488 
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 defined, as in the cases already men- 
tioned, and to be formed by a structure inde- 
pendent of the epithelium, which latter forms 
Aths of their thickness. This structure is the 
basement membrane. When masses of epithe- 
liam, 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 (fig. 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 (fig. 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 > Gym 
vessels are spread out, with a") a 
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 wie villi, to the dog ( Cant > 
support it, and form a “awa : 
of / ose remarkable shea gr le a 
tions. Nevertheless I have 
not been able to see it in an 4t@¢, Nem basement 
isolated and distinct form, Cetien ee 
and do not therefore assert  pulging 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 a high power, and 
Fig. 276. 
MUCOUS MEMBRANE. 
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 part 
within the villus. 
It might seem at first sight a hopeless t 
to search in so dense and complicated a stru 
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 u i 
brought into view, exceeds the 8000th of 
inch in thickness. But as it must exist, if at 
all, between the epidermis and the vessels i 
nerves of the cutis, in a position sufficientl 
determinate, much of the apparent difficult 
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 papillz) on its free sur-— 
face. The close resemblance these 
pille and the villi of mucous membranes has 
observed by many anatomists. The dis- 
tribution of the vessels within pee: essentially 
the same. Here, then, under epidermic 
layer, we might expect to find the 
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 ther 
examined the outline of the bare papille with 
a power of 300 diameters. This outline 1 
sharply defined, and appears to be Lec 
by a homogeneous membrane, enclosing the 
vascular and nervous contents. This mem. 
brane I believe to be that which I am 
describing, though, as in the case of the intes- 
tinal villi, 1 have never been able to isolate 1 
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, 
, 
¢ 
Part of the tubule of a sudoriferous gland fron 
Ml sotila. aay 320 diameters, 
A, transverse section ; B, side view of the inte 
obtained by bringing the axis of the tubule 
focus; a a a, basement membrane; b b 3, ¢ 
thelium ; cc, cavity of the tubule; d, super 
epithelial particles; e, dee epithelial particle 
A a detached superficial epithelial par 
shewing the nucleus and pigmentary gi 
g, its detached nucleus, with a nucleolus. 
