78 
PLIirr's NATUEAL HISTORY. 
[Book XI 
reunite, and if wounded, it is wonderful what excruciating 
pain they cause ; though, if completely cut asunder, they are 
productive of none whatever. Some animals are destitute of 
nerves, fish, for instance, the bodies of which are united by 
arteries, though even these are not to be found in the mol- 
lusks. Wherever there are nerves found, it is the inner ones 
that contract the limb, and the outer ones that extend it. 
Among the nerves lie concealed the arteries, which are 
so many passages for the spirit ; and upon these float the veins, 
as conduits for the blood. The pulsation of the arteries is 
more especially perceptible on the surface of the limbs, and 
afford indications of nearly every disease, being either statio- 
nary, quickened, or retarded, conformably to certain measures 
and metrical laws, which depend on the age of the patient, and 
which have been described with remarkable skill by Hero- 
philus, who has been looked upon as a prophet in the wondrous 
art of medicine. These indications, however, have been 
hitherto neglected, in consequence of their remarkable subtilty 
and minuteness, though, at the same time, it is by the observa- 
tion of the pulse, as being fast or slow, that the health of the 
body, as regulating life, is ascertained. 
CHAP. 89. — THE arteries; the VEiisrs: aistimals without 
ARTERIES OR VEINS. THE BLOOD AND THE SWEAT, 
The arteries are destitute of sensation, for thej are devoid of 
blood. They do not, all of them, however, contain the vital 
spirit, and when one of them has been cut, it is only that part 
of the body that is reduced to a torpid state. Birds have 
neither veins nor arteries, which is the case also with serpents, 
tortoises, and lizards ; and they have but a very small propor- 
tion of blood. The veins, which are dispersed beneath the 
whole skin in filaments of extreme thinness, terminate with 
such remarkable fineness, that the blood is able to penetrate no 
further, or, indeed, anything else, except an extremely subtle 
humour which oozes forth from the skin in innumerable small 
drops, and is known to us as sweat.*' The knot, and place 
of union of the veins, is the navel. 
CHAP. 90. (38.) ANIMALS, THE BLOOD OE WHICH COAGULATES 
WITH THE GREATEST RAPIDITY I OTHER ANIMALS, THE BLOOD 
OF WHICH DOES NOT COAGULATE. ANIMALS WHICH HAVE THE 
