491
GLAND.
most complicated glands he relied solely on
his vascular injections, to the exclusion of the
evidence afforded by the much more satisfactory
researches of comparative and developmental
anatomy. If, as Professor Miiller has ob¬
served, Ruysch had carefully examined his
injected organs with the microscope, he would
have found that between the most delicate
plexuses of the bloodvessels there is always
an additional substance destitute of vessels ;
although these organs, when seen by the naked
eye, appear to be stained in every direction
with the coloured injection.* But even ad¬
mitting what frequently happens from a too
forcible injection, that the matter thrown into
the arteries is found in the ducts, this does
not prove that the small bloodvessels are con¬
tinuous with the excretory canals; for after
the sanguiferous vessels are filled, they easily
become ruptured, and so allow their contents
to escape into the ducts. It may further be
objected, that in all the glandular organs which
have been carefully inspected the commence¬
ments of the excretory ducts are larger than
the least arteries ;f indeed, Ruysch’s own
account of this imaginary continuity is very
vague, and the plates designed to illustrate
his theory, especially that of the kidney, are
any thing but satisfactory. As Ruysch did
not employ the microscope, it is impossible
he could have seen that continuity which he
so confidently described; indeed, as Ilaller
remarks,X it is difficult, or rather as we should
say impossible, to demonstrate, with the aid
of the most powerful lens, the connexion of
the last arteries with the coats of the ducts.
Not only did Ruysch adopt a most in¬
sufficient mode in prosecuting his inquiries,
but he assumed as a fact what was in reality
a mere hypothesis, that secretion can only take
place from the open mouths or orifices of the
secerning arteries. The only point, therefore,
which he discussed was, whether the passage
of the arteries into the excretory ducts takes
place gradually and insensibly, or suddenly
and by the intervention of a follicle; for it
never occurred to the anatomists of those times,
or even to Haller and his contemporaries, that
canals closed at their end by cul-de-sac, and
without open arterial mouths, could secrete.§
* Loc. cit. p. 8, § 4.
t Diameter of secreting canals.
Line
Parotid gland . . . 0-0099 (Weber).
Kidney .... 0'0166 (Meckel).
Ditto.....0-0180 (Weber).
Testis .... 0 0564 (Miiller).
Ditto..... 0-0648 (Lanth).
Liver (in rabbits) . . 0 0140 (Miiller).
Diameter of capillary bloodvessels.
Line Line
Parotid . . 0 0030 to 0-0039 (Weber).
Kidney . . 0-0044 to 0-0069 (Müller).
Testis . . . 0-0030 to 0-0035 (Weber).
Burdach Physiol. Fünfter Band. p. 38. For
measurements in other glands, see Müller De
Gland. Struct, p. 112 ; Valentin Handb. der En-
twickelungs-geschichte, p. 535 et seq.
t El. Phy. t. ii. p. 378.
$ The existence of open mouths in the arteries
of the serous membranes, where they are generally
But the true opinions of Malpighi did not
refer to the exact mode of termination pos¬
sessed by the arteries; nor did he imagine
that any particular machine or follicle was
interposed between the arteries and the ducts :
his observations were rather directed to the
more important circumstances relative to the
disposition, formation, and extent of the true
secreting canals.
In concluding these remarks on the hypo¬
thesis of Malpighi, it is due to the character
of that illustrious cultivator of anatomical sci¬
ence to state that his views are highly phi¬
losophic, and in a general manner correct—
that they are supported by numerous obser¬
vations made on the glands of the lower ani¬
mals, as well as on the development of the
liver during incubation—and that he had thus
the sagacity to adopt the mode, which expe¬
rience has shown is alone capable of resolving
this difficult question.
It would be superfluous to enter into a de¬
tailed account of the opinions advanced by
later anatomists, as they are for the most part
simply modifications of the hypothesis either
of Malpighi or of Ruysch. A few general
observations will therefore suffice.
Ferrein has the merit of being the first wri¬
ter who pointed out in a more distinct manner
than had been done by Malpighi, the great
importance of what are erroneously called the
excretory duets, but which constitute, as we
have already shown, the true secerning struc¬
ture. He remarks * that the cortical part of the
kidney is composed of a collection of white
cylindrical tubes, variously folded on them¬
selves (canales corticales, or ducts of Ferrein,)
and he thought he had seen the same tubes in
the liver. The serpentine cortical canals have
been seen in birds by Galvani, to be filled with
cretaceous urine after the ligature of the ureter.
Although the researches of Ferrein are very
important, yet they want that support from
comparative anatomy, by which means alone
they could have been made subservient to esta¬
blish any general principles.
To Rolando belongs the honour of having
demonstrated the mode in which the glands
are developed from the alimentary canal. By
carefully conducted observations on the in¬
cubated egg, he discovered that each of these
organs in the first instance consists of an ele¬
vation or tubercle of the intestine, which sub¬
sequently becomes hollowed and forms a canal
directly continuous with that of the intestine.
He also distinctly announced what has since
been demonstrated in all its details, that the
lungs are formed, like the glands, by a pushing
out of the upper end of the intestinal tube;
and he further describes the mode in which
the bronchi and their subdivisions are deve¬
loped. The error of those writers who contend
called exhalants, has never been proved ; on the
contrary, on examining, with a powerful micro*
scope, the circulation of the peritoneum in rabbits,
I have repeatedly observed that the small arteries,
after ramifying in a very complicated manner,
become distinctly continuous with the little veins.
* Mem. de l’Acad. Roy. des Sc. 1749 p. 492 '
