iaphragm is more arched before than
after respiration, and rises higher in the thorax in the former case
than in the latter. The lungs before respiration are situated in the
back of the thorax, and do not fill that cavity; they are of a dark,
red-brown colour and of the consistence of liver, without mottling.
After respiration they expand and occupy the whole thorax, and closely
surround the heart and thymus gland. The portions containing air are of
a light brick-red colour, and crepitate under the finger. The lungs are
mottled from the presence of islands of aerated tissue, surrounded by
arteries and veins. The weight of the lungs before respiration is about
550 grains, after an hour's respiration 900 grains; but this test is of
little value. The ratio of the weight of the lungs to that of the body
(Ploucquet's test), which is also unreliable, is, before respiration,
about 1 to 70; after, 1 to 35. Lungs in which respiration has taken
place float in water; those in which it has not, sink. There are
exceptions to this rule, on which, however, is founded the _hydrostatic
test_. As originally performed, this test consisted merely in placing
the lungs, with or without the heart, in water, and noticing whether
they sank or floated. The test is now modified by squeezing, and by
cutting the lungs up into pieces.

The objections to the test as originally performed are--(1) That the
lungs may sink as the result of disease--_e.g._, double pneumonia. (2)
That respiration may have been so limited in extent that the lungs may
sink, owing to large portions of lung tissue remaining unexpanded
(_atelectasis_). (3) Putrefaction may cause the lungs to float when
respiration has not taken place. (4) The lungs may have been inflated
artificially. Few of these objections apply, however, when the
hydrostatic test, modified by pressure, is employed. To take these
objections in detail, it may be stated: (1) If the lungs sink from
disease, the question of live birth is answered. (2) This objection is
too refined for practical use. The lungs sink, there is an absence of
any of the signs of suffocation, and the matter ends. The examiner has
only to describe the conditions which he finds, and is not required to
indulge in conjectures as to the amount of respiration which may or may
not have taken place. (3) Gas due to putrefaction collects under the
pleural membrane, and can be expelled by pressure, and is not found in
the air cells. The lungs dec