d ensue were any
ordinary air-breathing animal subjected to such changes of pressure.
Man can endure without suffering an increase of pressure of the gases
in his body amounting to three or four times that to which he is
accustomed, as, for instance, when working in the compressed air of
"caissons." But the whale goes suddenly to a depth at which the
pressure is eighty times that at the surface! Then, too, man (and
other terrestrial animals), after being subjected (for instance, in a
caisson) to a pressure of four times that which exists on the free
surface of the earth, is liable to be killed by suddenly passing from
that high pressure into the ordinary air. The gases dissolved in his
blood expand like the gas in a bottle of soda-water when the cork is
drawn, and the bubbles interfere with the circulation of the blood in
the finer blood-vessels (of especial importance being those of the
brain and spinal cord), and the serious illness and the death of
workmen has frequently resulted from this cause. Accordingly, the men
who work in such "compressed atmospheres" are now made to pass slowly
through a series of three chambers, in each of which the pressure is
diminished and brought nearer to that of the normal atmosphere. By
spending twenty minutes in each chamber successively, the workman is
gradually brought to the pressure of the outer world, and his blood
prevented from "effervescing." But what must be the condition of the
gases in the blood of a whale which suddenly rises from 400 fathoms to
the surface? The whale suddenly goes, not from a pressure of four
times the normal ("four atmospheres," as it is called), but from
eighty times the normal, to the normal pressure.

Whales, and also seals, are provided with remarkable special networks
of blood-vessels in various parts of the body (called "retia
mirabilia" by the old anatomists,) and also with a thick layer of fat
under the skin, the "blubber" (some feet deep in a large whale), full
of blood-vessels. It has been suggested that these networks of
blood-vessels are related in some way both to the power of keeping
long (forty minutes!) under water without breathing, and also to the
freedom of these marine monsters from the deadly effects of rapid
passage from great to little gas-pressure. But it is only a
suggestion; no one has shown how the networks can act so as to effect
these results, and I am quite unable to say how they do so. Another
suggestion worth considering