THE vse of the great Artery and of his branches may bee considered two wayes; eyther as they are Canales or Pipes, or as they mooue and beate * 1.1 perpetually. As they are Canales or Pipes they haue three vses or ends. First to contayne spirituous and vitall bloud, and to distribute it vnto the whole body, partly for the perfect nourishment of the particular parts, * 1.2 for the parts, sayth Galen in the tenth chapter of his sixt Booke de vsu partium, which are neare vnto the Arteries doe draw out of thē vaporous bloud though it be but little; partly for the nourishment and generation of the animall spirits.
The second vse is to leade vnto the parts vital spirits, to cherish and sustaine those vi∣tall spirits which are seated in the parts. Thirdly, with the same spirit to transmit heate and the vitall faculty perpetually into the whole body, to cherish the in-bred heat of the particular parts, to moderate and gouerne their vitall functions and to defend their life.
As the Arteries doe beate, so haue they also a treble vse. The first is to preserue the in-bred heat of all the members which they do by ventilation or wafting ayre vnto them. * 1.3 For if it were not breathed it would by degrees languish and be extinguished. Their se∣cond vse is by their motion to make a kinde of commotion in the bloud (for the arteries accompany the veines) which if it were at rest would putrifie like standing waters, for bloud sayeth Hippocrates is water. The third vse is to solliciate and to compell the bloud to fall out of the veines into the substance of the parts for more speedy nourishment.
This motion of the Arteries is called pulsus or pulsation (of the worde Hippocrates * 1.4 as Galen witnesseth was the first authour) which is absolued by dilatation and contracti∣on: qualities not bred with the artery or seated in their substance, but flowing into them from the heart, which may be demonstrated if you intercept a part of an arterie with a tie, for the part that is vnder the tye will haue no motion, but as soone as the tye is taken a∣way the motion will returne.
Erasistratus conceiued that the Arteries mooued quite contrary vnto the motion of the heart: but wee agree rather with Herophilus, Aristotle and Galen, who thinke they are dilated and constringed in the Diastole and Systole of the heart: onely we must remember, that the motion of the heart is swifter and more vehement then that of the arteries, which you may thus make experience off. Lay your right hand vpon your heart, and with your left hand touch the wrest of the right hand, and then you shall perceiue whether the mo∣tion of both bee the same or contrary, but the more certaine knowledge of this poynt is taken from the dissection of liuing creatures.
In the contraction of the Arteries they strongly driue vital spirits into the whole bo∣dy