LACTEALS IN THE VILLI.
271
escape of the red particles of the blood from the capillaries. All
good observers agree that there are no visible openings in the villi of
the intestines; and I have myself repeatedly examined the villi of
the intestines of the calf, ox, rabbit, hog, and cat, without having
even perceived any perforation in their extremity. No opening
certainly exists at that part of the villi.
Structure of the intestinal villi.—The villi of the intestines are
short processes, a quarter of a line to a line, or at most a line and
two-thirds in length, rising from the surface of the mucous membrane,
and giving this membrane, when magnified, the appearance of a
thick fleece. Their form is sometimes cy lindrical, sometimes lamellar,
and frequently pyramidal.
Rudolphi at first believed that the villi were devoid of blood-vessels,
and A. Meckel imagined that all the injection which entered them
did so by imbibition or extravasation. Meckel could not have had
before him good preparations of injected villi when he came to this
conclusion. Not only can the vessels of the villi be beautifully shown
by injection, as Doellinger, Seiler, and Lauth have described and
represented, but I have, with the naked eye as well as with a lens,
seen them filled with blood. Once I observed this in the calf, and
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afterwards in the dog, the intestine being examined immediately after
death before it was washed.
The extremity of the villi presents the same delicate texture as the
rest of their surface. The assertion of Bleuland and others, that they
had an opening at their extremity, was refuted by Rudolphi, who ex¬
pressed all that has hitherto been known of the structure of these
parts in the following words:—“ They have never any visible open¬
ing; in their interior there is a network of blood-vessels, which can
seldom be demonstrated, however, except by injection; and the
lacteals also take their rise by a network within the villi.”
It appears to me to be an important circumstance, that the villi are
in part hollow, and are formed of an exceedingly delicate membrane
in which blood-vessels ramify. The simple cavity I have found prin¬
cipally in the cylindrical villi. By comparison I have ascertained that
the thickness of the membrane which forms the villi in the calf is
-j4öth of an inch, and the diameter of the capillary blood-vessels
which run in this membrane, may be reckoned at from -jy^th t0
TsVoth of an inch. An opportunity occurred, recently, at the dis¬
secting-rooms in Berlin, of examining the villi of intestines in which
the lacteals were filled with chyle in the human subject. They were
found to contain a simple cavity running from base to apex. This
was proved both by the microscopic examination of the villi by
Henle, and by their injection with mercury by Schwann, who forced
the mercury into the lacteals which were distinctly visible in the
mucous coat, and thus filled the villi even to their closed extremity.
There is something of a very different nature, which might be mis¬
taken for hollow villi. This is a kind of epithelium, but of extreme
delicacy. It is not solid, like an epidermis; on the contrary, although
coherent in a membranous form, it is so nearly allied to mucus, that
it seems to me to be a secretion intermediate between epithelium and
mucus.