74 ON THE MOTION OF THE BLOOD. 



127. We must now enquire what powers are excited 

 by other organs in assisting the circulation. The exist- 

 ence of some secondary powers and their ability to as- 

 sist, or even in some cases to compensate for, the 

 action of the heart, are proved by several arguments : 

 v. c. the blood moves in some parts to which the in- 

 fluence of the heart cannot reach, in the vena portae 

 and placenta ; not to mention instances of the absence 

 of the heart.* 



128. The principal of these powers is the function of 

 the arteries, not easy indeed to be clearly understood 

 and demonstrated. 1. They have a muscular coat. (E) 

 2. That they are irritable, has been proved by repeated 

 experiments, t 3. The size of the soft nerves arising 

 from the sympathetic, and surrounding the larger arte- 

 rial branches, particularly in the lower part of the 

 abdomen, argues the importance of these vessels in 

 assisting the motion of the blood. 



129. The arteries pulsate, and indeed violently, so 



* See v. c. C. W. Curtius. De motistro huma.no cum infante gemello. Lugd. 

 Bat. 1762. 4to. p. 39. W. Cooper, Philos. Transact, vol. Ixv. p. 316. 

 Haller, Opera Minor a. T. iii. p. 33. C. Chr. Klein, Descriptio momtrorum 

 qvorundam. Stuttg. 1793. 4to. 



f- Walter Verschuir, De arteriar. et venar. vi irritabili ; ejusque in vasts 

 excessu; et inde oriunda sanguiws dircctione abnormi. Groning. 1766. 4to. 



Rich. Dennison, Diss. arterias omncs ft venarum partem irritabilitate pree- 

 ditas esse. Edinb. 1775. 8vo. 



Chr. Kramp, De vi vitali arteriarum. Argent. 1785. 8vo. 



1 Observe for instance, in Walter's Tabula nervor. thorac. et abdominis, the 

 rizht hepatic, Tab. ii. O. Tab. iii. /. the splenic, tab. ii. P. Tab. iii. i. tab. 

 iv. o. the superior mesenteric, Tab. ii. Q. Tab. iii. s. the inferior mesenteric, 

 Tab. ii. T. and many others. Compare Soemmerring, De c. h. fabrica. 

 T. iv. p. 362. 



Haller, DC Nervor. in arterias imperio. Getting. 1744. 4to. Luca; I.e. 



