f oxygen, in the lungs; and as
the absorption of oxygen is a cause of solidity in many bodies, this
tenuity of the blood may proceed from a deficient absorption of
oxygen. However this may be, it is certain that the blood is very much
attenuated, though with considerable variations in degree, as it is
sometimes found thin on opening a vein, and at a subsequent period is
thicker; varying perhaps according to the continuance of ease or
difficulty in respiration. It is certain, that this attenuation of the
blood must tend to an increase of the serous exhalations.

That these secondary dropsies are not the effect of debility appears
pretty evident from considering, that they often exist while the
strength of the patient is yet undiminished, while all the other
secretions, except that of the urine, are carried on with vigour, and
while the appetite and digestive functions are not only unimpaired,
but improved.

The examinations of the _ninth_ and _tenth cases_ are particularly
valuable, because they confirm what had been observed in other
subjects; they exhibit two well marked instances of aneurism of the
heart, and present us a view of organic disease unattended by dropsy
of the pleura. This must be sufficient to remove the suspicion, that
the symptoms we have attributed to the former disease might arise from
the existence of the latter. No one probably will be willing to impute
a chronic disease, terminated by a sudden death, to five or six ounces
of water in the pericardium; for such a quantity, though it might
produce inconvenience, could not prove fatal, unless it were suddenly
effused; and, if this were true, it of course could not have been the
cause of the long train of symptoms observed in _case tenth_.

Dr. William Hamilton, the author of a valuable treatise on the
digitalis purpurea, thinks the hydrothorax a more frequent disease
than has commonly been imagined, because he conceives that it has
often been mistaken for organic disease of the heart. He names, with
some precision, many symptoms of the latter complaint; but how remote
he is from an accurate knowledge of it may be discovered by his
opinion, that, in diseases of the heart, "the patient can lie down
with ease, and seldom experiences much difficulty of breathing." The
limits of this paper do not admit a discussion of this and other
points, respecting which he seems to be mistaken. We must therefore
submit them to be decided by the evidence adduced in D