cumstances ; and in some experiments performed
with the view of determining this point, I found
that although sensation and motion had entirely
ceased, and the animal had become rigid and
apparently dead, the action of the heart still continued.
It occurred to me at such a moment to
place the lung of the animal under the object glass
of the microscrope. I was highly gratified to find
its circulation, arterial, capillary and venous, quite
perfect! I had thus an opportunity of contemplating
at leisure, in one instance during four successive
hours, under circumstances free from the
infliction of pain or suffering, this most splendid
and interesting scene.
I have subsequently found that water of the temperature
of 120°. of Fahr. answers far better than
water at 108°. The hatrachia plunged into water
of 120°. die to sensation and motion almost instantaneously.
The salamander and the toad are the hatrachia
which are most to be preferred for this experiment.
The lung of the former is most easily maintained
distended, and displays the most simple circulation.
The toad is far more tenacious of vascular life, and
displays the beautiful phenomena of the circulation
r a p H H ■ wMa* BMP
for a much greater length of time. The lung of the
frog is very apt to collapse. It is necessary, therefore,
to adopt another device when we wish to
watch the pulmonary circulation in this species :
the lung must first be moderately distended with
air, by means of the blowpipe inserted into the
larynx; the larynx must then be secured by a
ligature. It is equally necessary to avoid too
great distention of the lung, and all stricture upon
its root as it passes out of the orifice made into the
"body of the animal; for then the circulation will be
much impaired, or even totally arrested.
I. Of THE MINUTE AND CAPILLARY VESSELS
OF THE SYSTEMIC CIRCULATION.
It is always perfectly obvious that the distribution
of the vessels is strictly appropriate to
the peculiar office, which they have to perform
in each individual part or organ. The anatomy,
as Mr. Charles Bell has so well pointed out,
constantly suggests the physiology ; and in no
case is this remark more distinctly verified, than
in the peculiarities of the minute and capillary