' 'jl 
496 DR. PHILIP ON THE CIRCULATION OF THE BLOOD. 
jections Dr. Young observes, that a part may be muscular although it does 
not contain fibrin, and refers in support of this opinion to the crystalline lens. 
The former of these objections no longer exists, the vessels having been found 
to obey both stimulants and sedatives as readily as parts more evidently mus- 
cular. It appears from many experiments related in my Treatise on the Vital 
Functions, that the action of the capillary vessels is as easily influenced both 
by stimulants and sedatives as the heart itself; and although the larger vessels 
are not so easily excited artificially as the heart and muscles of voluntary 
motion, yet several physiologists have succeeded in exciting them both by 
mechanical and chemical agents. But there is another argument in favour of 
the muscularity of the vessels, which, I think, may be regarded as no less 
powerful. I endeavoured, in papers which I had the honour to present to the 
Society, and which appeared in the Philosophical Transactions for 1815, to 
ascertain the relation which the heart bears to the nervous system, which is 
different from that of the muscles of voluntary motion. It appears from the 
facts there adduced, that this organ is not only independent of that system, 
although capable of being influenced through it either by means of stimu- 
lants or sedatives, and that even to the instantaneous destruction of its power; 
but that it equally obeys either set of agents, whether applied to the brain or 
spinal marrow ; while the muscles of voluntary motion obey no stimulus acting 
through the nervous system, unless it be applied to their nerves themselves or to 
the particular parts of that system from which their nerves arise. I found from 
repeated experiments that the vessels bear the same relation to the nervous 
system as the heart does, their power being independent of this system, but 
equally with the heart capable of being influenced by either stimulants or 
sedatives applied either to the brain or spinal marrow, and that even to the 
instantaneous destruction of their power. They in all respects bear the same 
relation to the nervous system with the heart, which affords the strongest 
argument for believing that their power is of the same nature*. 
From the various facts stated or referred to in the foregoing paper, the fol- 
lowing inferences appear to be unavoidable ; — That the circulation is main- 
tained by the combined power of the heart and blood-vessels; and that the 
power of both is a muscular power. 
* My Treatise on the Vital Functions. 
