These distinctions are highly important. Without
them, the phenomena cannot be clearly described
or understood. It is quite erroneous to speak of
capillary arteries, or capillary veins, or of the true
capillary vessels as a venous net-work, as vessels
containing a serous blood without globules, or as
rather to be inferred than accurately seen. The
last branches of the arterial system and the first
roots of the venous, may be denominated minute;
but the term capillary must be reserved and
appropriated to designate vessels of a distinct
character and order, and of an intermediate
station, carrying red,globules, and perfectly visible
by means of the microscope. Meckel is obviously
in error, in omitting to mention the capillaries
altogether ; and Adelon, in speaking of the capillary
systems in the plural number, including under
that designation the nutrient, secretory, and
exhalent vessels.
Having made these preliminary remarks, I must
revert to the plan devised for placing the moving
blood in the field of the microscope to which I have
alluded; for it is in this manner alone that the
minute and capillary vessels can be traced.
It was a point of singular interest to ascertain
whether there were any characteristic differences
between the systemic and pulmonary minute and
capillary vessels and circulation, and in the different
parts of each of these. In order to institute
the requisite comparison, in the same and in
different animals, it was necessary that the lung and
the mesentery should be placed under the microscope,
and that the circulation should continue
for a sufficient time unimpeded and undisturbed.
The struggles of the animal during life, with the idea
of its sufferings, would effectually have frustrated
this object. It was, therefore, with no slight
degree of satisfaction that I was enabled to devise
a mode of annihilating the sensation and arresting
the motions of the animal whilst the circulation
was preserved entire.
The mode of proceeding to which I have alluded,
is founded upon an interesting observation of M.
Edwards,1 that the batrachian reptiles, placed in
water of 42° of the centigrade thermometer, or 108°
of Fahrenheit, die almost immediately. It was an
interesting point to ascertain the cause of so sudden
an annihilation of life in these animals in such cir-
1 De 1 'Influence des Agens Physiques Sur la Vie; par M. F.
Edwards, D. M. &c. 'A Paris, 1824.
C 2