82 ON THE MOTION OF THE BLOOD. 



contraction immediately occurring on making a puncture in a 

 portion of vessel included between two ligatures. The capacities 

 of arteries are thus always accommodated to the quantity of 

 blood, and this circumstance gives the arterial canal such pro- 

 perties of a rigid tube as enable an impulse at the mouth of the 

 aorta to be instantly communicated throughout the canal. This 

 appears the great office of the contractile powers of arteries, for,, 



(F) They do not incessantly dilate and contract as many ima- 

 gine. Dr. Parry, on the most careful examination, could nevei- 

 discover the least dilatation in them, during the systole of the 

 ventricle, when the pulse is felt. He very properly remarks, 

 that the pulse is felt only when arteries are more or less com- 

 pressed ; under which circumstance, the motion of the blood 

 onwards, by the impulse of a, fresh portion from the left ven- 

 tricle, is impeded : and this effort of the fluid against the ob- 

 structing cause gives the sensation called the pulse.* 



Dr. Curry, the late senior physician and highly distinguished 

 lecturer on the practice of medicine at Guy's Hospital, concluded, 

 without doubt hypothetically, from some microscopic experi- 

 ments which he made on inflammation in the presence once of 

 Mr. Charles Bell and once of Mr. T ravers, that the circulation 

 is indispensably facilitated by a sort of electric repulsion between 

 the vessels and their contents, and that in inflammatory accu- 

 mulation, the tone of the vessels being impaired, this repulsien 

 is diminished and the blood passes onwards with difficulty in 

 consequence. My friend and colleague Dr. Scott has obliged 

 me with ample notes taken by himself some years ago, but any 

 one may see in the edition of Dr. Curry's Syllabus, printed in 1810, 

 page 6G, the paragraph in which inflammation is referred to the 



* An Experimental Enquiry into the Nature, Causes, and Varieties of the 

 Arterial Pulse , &c. by Caleb Hillier Parry, M. D. F.R.S. 1816. Likewise a 

 second work, entitled, Additional Experiments on the strteries of wfrrm 

 blooded animals, &c. by Chas. Hen. Parry, M.D. F.R.S. 1819. the latter displays 

 as much talent and learning as the former of originality. Dr. Young:, in a 

 Croonian lecture, highly worth perusal, on th? Functions of the Heart tnt' f 

 Jifoorl Ft-.w&, reasons forcibly to prove that the muscular power of arterie*. 

 has very little effect in propelling the blood. Phil. Trans. 1809. 



