500 
their course have not (in man) any proper wall, 
but are bounded only by the edges of the scales 
between which they pass, it is very probable 
that the deeper and softer lamine of epidermic 
particles may not merely be moistened by the 
secretion of the ducts, but, under favourable 
circumstances, may borrow extraneous matters 
from them, and thus become a part of the ab- 
sorbing medium. In reference to the question 
of absorption by the skin, it is interesting to 
notice the modification of this structure in those 
lower animals in which this function is mani- 
fested in much greater activity than in man. 
A better example cannot, perhaps, be selected 
for this purpose than that of the frog. Its epi- 
dermis consists of a single layer of scales, and 
in consequence they do not overlap, but join 
edge to edge. These scales are not reduced to 
mere membrane, but always contain a con- 
siderable quantity of fluid in their interior. 
The sweat-pores open here and there in the 
interstices between three scales, and have true 
walls, formed out of a pair of modified epi- 
dermic particles, adapted to one another, and 
elongated into the subcutaneous texture. They 
thus bear a very close resemblance to the 
stomata of leaves. I lately discovered this 
singular arrangement in the cast-off cuticle of 
the animal. It seems undeniable, that, here, 
absorption is effected by the whole series of 
epidermic scales, as well as by the pores. _ 
. But the most remarkable, and at the sametime 
the most recondite form, under which this func- 
tion is exhibited in the mucous system, is that 
met with in the alimentary tract. Here, indeed, 
water and aqueous solutions are imbibed, with 
great rapidity, into the vascular plexuses of the 
blood and lacteal systems, as the united testi- 
mony of many able experimenters abundantly 
shews. But from this merely physical process 
of imbibition is to be distinguished the more 
mysterious and elective function of chylous 
absorption, which is conducted by the lacteals 
alone, and is consequently limited to the region 
supplied with that system of vessels. For an 
account of the present state of knowledge on 
the highly important subject of the intimate 
nature of this function, the reader is referred 
to Apsorprion and Lympuartic System, in 
which he will find the chief of the conflicting 
statements and opinions of physiologists de- 
tailed and discussed. It has already been ex- 
plained in the present article, that the latest 
observations on the structure of the villi, and 
apparently the most exact ones, because con- 
ducted with the most improved lenses, and 
accordant with other collateral discoveries, make 
it highly probable that the opinion assigning 
open mouths to the lacteals is erroneous. In 
_ the description of those orifices, furnished by 
Treviranus, we may plainly discern his partial 
acquaintance with characters which we now 
know to be those of the prismatic epithelium 
investing the villi; and the less precise asser- 
tions of the same kind by several other excel- 
lent anatomists, we may now, perhaps, fairly 
consider to have been founded on deceptive 
appearances which, in their day, did not admit 
of secusie interpretation. If any such orifices 
MUCOUS MEMBRANE. 4a 
exist, their minuteness must be extreme, and — 
they? must lie in the intervals between pe 
prisms of epithelium. But even such attenu-— 
ated pores, the best microscopes fail to detect, 
and at least it may with certainty be affirmed, 
that none large enough to admit a chyle-globule — 
exist. The structure of the villi, no less than 
our knowledge of the absorbent function im 
eneral, seems to indicate that the chyle, when — 
rst taken up, is strictly a fluid, and only ac- 
quires its solid particles after it has entered Sh 
lacteal plexus. ee 
Of the separation of material from the body 
—This function appears to be carried on 
every part of the mucous system. One great 
division, that of the glands, is specially des- 
tined to it, as are likewise those portions of th 
compound mucous membranes, which ha 
been already described as coming prope: 
under the designation of glands. If, he 
the essential nature of the function of secretion 
be adequately considered, it will scarcely be 
doubted that even the simplest parte of the 
mucous membranes, and the whole cutaneous 
surface (as distinguished from its sebaceous 
— 
and perspiratory glandular offsets) share largely 
in this important office. It is true that in the 
skin this function holds a subordinate place to 
that of defence and protection, but its existen 
is only an example of what an attentive survey 
of nature everywhere discovers; the accom- 
plishment of various ends by means of the 
same simple instruments. p 
The notion that a secreted product must be 
fluid, is one that has arisen out of a partia 
and imperfect insight into the nature of the 
secreting process. Those matters which 
eliminated in the largest quantities and by th 
largest glands are for the most part so, in th 
shape under which they meet the eye, that is 
after their separation from the organ in whic 
thev are secerned. But in the case of the lung 
the secretion is gaseous as well as fluid, and in 
numerous instances, which have been recent 
brought to light, chiefly by the labours « 
Henle, it is found, when minutely seru 
nized, to consist of organic forms entitled t 
be styled solid. 
The problem which physiologists have ne 
to resolve, is how far these organic for 
which are more or less altered epithelial pr 
ticles, are necessarily concerned in the 
formance of the function, for epithelium is 
but universal in the mucous system. It wor 
be foreign to the province of this articl 
enter at length on the general question of se 
tion, and I shall confine myself to a few 
marks tending to show in what direction re 
researches point.* e 
When the secretion of a sebaceous follich 
the skin is minutely examined, it is foun 
consist entirely of epithelial particles co 
ing the sebaceous matter, and more or 
broken and compressed, These are simili 
the particles lining the follicle, and are m 
* Purkinje, Isis 1838, No. 7. Schwann, Fro1 
notiz. Feb. 1838. Henle, Miiller’s Archi 
P 104-8, 1839, p. 45; also Miiller’s Phys. 
aly, 2nd edit., vol. i., p. 503-4, ie 
ty 
*, 2 
£ 
4 
