78 plint'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 AETEEIES; THE VEINS: ANIMALS WITHOUT 



AETEE1ES OE VEINS. THE BLOOD AND THE SWEAT. 



The arteries are destitute of sensation, for they 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 OF WHICH COAGULATES 



WITH IHE GEEATEST EAPIDITT : OTHEE ANIMALS, THE BLOOD 

 OF WHICH DOES NOT COAGULATE. ANIMALS WHICH HAVE THE 



