blood, to or from the vessel, which alone demonstrates
the difference. A similar distribution of
* arterial, venous, and capillary vessels takes place
over the surface of the vertical meshes, as is
obvious from an oblique view of the membrane
carefully dried so as to preserve the appearance of
its vessels and of the globules of blood.
3. Of the Circulation in the Lung of the Toad;
— the Rana Bufo of L in n a e u s .
The structure of the lung of the toad is very
similar to that of the lung of the frog. The distribution
of its larger vessels is, however, singularly
different. The artery, as well as the vein, pursues
its course along the internal or central borders of
the vertical meshes.
The toad offers an advantage over the frog, as
the subject of investigations into the nature of the
pulmonary circulation. Its lung remains distended,
without the application of a ligature to
the larynx. And although sensation and motion
have entirely ceased, the beat of the heart and
even the circulation in the lung are perfect during
many hours. It was on this account that this
animal was chosen, in order, that an accurate
sketch might be taken of the pulmonary capillary
circulation.
The pulmonary circulation was very vivid during
four hours, in the case in which the .sketch,
Plate VIII., was taken. This sketch may therefore
be considered as most accurate. The course of
the blood in the capillaries is marked by arrows,
so that the arteries and the veins can be readily
distinguished.
It would not become me to speak of the
merits of any performance of my own. But I
believe I may say that there is not, in any
published work, any accurate account of the
minute and capillary wessels and circulation, or
any account at all of the minute and capillary
circulation of the lungs.
It is singular, that in the midst of the dispute
concerning the irritability of the capillaries,
there should be a doubt whether these vessels be
real tubes or mere canals. There are many
reasons which incline me to the latter opinion.
It is a further point in minute anatomy, highly
interesting and important, and deserving of the
most assiduous research.