220 ON THE CIRCULATION IN 
and the blunt hook of a spring scale was caught in the upper jaw, the other end of the 
scale being also secured to the table. During this time the Turtle’s head was held extended. 
When it was released the animal drew it briskly into the cover of the shell, thus pulling 
on the scale until the index-point marked fifty-seven pounds as the force of the pull made 
by the retracted neck. Nearly equal vigor was manifested by others of the same species, 
and all were so active that by extending the head and using their powerful tails they were 
able to right themselves with ease, when placed on their backs, a position in which the 
Green Turtle becomes altogether powerless. 
The length of life in the separated head of the Snapper, and its power to bite long 
after being removed from the rest of the body, is very well known, but the astonishing 
resistance of the animal to one of our most active poisons is a still better test of its great 
and enduring vital power. So remarkable indeed was this, that I have studied it with 
some care, and described it at length in a separate paper. At present it will suffice to 
relate a single experiment illustrating the point in question. 
Assuming M. Bernard’s experiments” as a basis, if a Snapper weighing twenty-six pounds 
were a warm-blooded creature, it would be killed by the injection into its veins of about 
one-tenth of a grain of woorara. On several occasions I have injected into the jugular 
veins of Turtles weighing from twenty to twenty-seven pounds, thirty times this amount. 
The animal became motionless within five minutes, but soon began to recover, and at the 
close of twenty-four hours was, in several instances, as well as ever. As the heart’s action 
is not primarily checked by this poison, which acts only on the motor nerves, it is gradu- 
ally eliminated, and after some hours the power to move the respiratory muscles returning, 
the Turtle gradually recovers all its usual activity; the limit of endurance being the 
length of time during which the reptile can exist without renewing its supply of oxygen. 
I have occasionally seen Turtles weighing two or three pounds, so poisoned with woorara 
as to remain motionless and without the least reflex movement during three days, after 
which life and action gradually but completely returned. 
It will thus be seen that for strength and tenacity of life, the Snapper is well suited to 
exhibit a type of reptilian blood-pressures. 
The following points were made the subjects of study: 
Ist. The arterial pressure. 
2d. The force of the heart’s contraction. 
3d. ‘The effect of inspiration and expiration on the arterial pressure. 
4th. ‘The influence of muscular motion on the arterial blood-pressure. 
dth. The blood-pressure in the central and distal ends of divided veins. 
6th. The effect of muscular exertion on the venous pressures. 
* Sur les substances toxiques, etc. Paris, 1857, p. 835. 
