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BRITISH ASSOCIATION.— 1835 . 
sank to the bottom like a stone. And are we to suppose that a de¬ 
gree of pressure under water, sufficient to soak in an instant every 
pore in the planks of a large boat, was not felt by the animal which 
dragged it to such a depth ? There can be little doubt that the 
application of this pressure would repel the fluids from the vessels 
near the surface of the animal into those more removed from its in¬ 
fluence in the deeper recesses of its body; that, in fact, an effect 
would follow, the opposite of that which is produced in an animal 
when placed under the exhausted receiver of an air-pump ; or such 
as occurs in persons attaining so high an elevation in the atmosphere 
as to be freed from some of its weight, in whom the blood is deter¬ 
mined to the surface, producing giddiness, bleeding from the nose, 
ears, lungs, &c. 
We may consider, therefore, that aquatic mammalia can exist with 
impunity during periods of suspended respiration, and also under 
degrees of pressure which would be destructive to the lives of ani¬ 
mals of the same class whose element is exclusively the atmosphere. 
And this may be considered still more remarkable, when it is recol¬ 
lected that during those periods of breathlessness and universal pres¬ 
sure, the voluntary and rapid movements which these animals perform 
when in pursuit of their prey, tend to urge towards the lungs, where 
the principal obstruction exists, all the fluids contained in the veins 
among the muscular structures of the body. 
The object of Dr. Houston’s communication is to point out the 
provision on which these peculiar diving faculties of such animals 
depend ; a provision beautifully harmonizing with all our physiolo¬ 
gical notions, and admirably adapted to the end in view. It consists 
of reservoirs connected with the veins leading to the lungs, where 
the blood may find a temporary resting-place during the period at 
which the asphyxiated condition of these organs refuses it transmis¬ 
sion through the vessels. Dr. Houston exhibited numerous prepara¬ 
tions and drawings demonstrating the presence of this singular 
provision in the porpoise, seal, otter, great northern diver, gannet, 
& c. The veins principally concerned in these dilatations are those 
nearest the heart, viz. the venss cavee, the venee cavee hepaticae, the 
jugulars, the veins of the spine, and those in the posterior regions of 
the abdomen. In the seal the venae hepaticae form large bags in the 
liver; and in the same animal there is on the back, and along the 
sides, and posterior part of the neck, a plexus of veins of such size, 
that, when they are filled with injection, the parts beneath cease to 
be visible; the vessels are as thick as the finger, and coiled, and 
heaped up on one another to an almost incredible amount. The 
contrast between the condition of the venous system in the great 
northern diver and that in the gannet, as exhibited by Dr. Houston, 
is important in establishing the uses of these reservoirs. 
The diver and gannet are both seafaring birds, but differ remark¬ 
ably in their modes of seizing the fish on which they feed. The diver 
swims under water after its prey, and remains at such periods long 
out of sight; the gannet pounces on it like an eagle, when discovered 
by its quick-sighted eye near the surface of the water, and thence 
