ON THE FUNCTIONS OF THE HEART AND ARTERIESc J]^ 



means of a true peristaltic motion. It appears also from apparently 

 the observations of Spaliawzani, that in many animals a nfoUon "* "^ 

 portion of the aorta, next the heart, is capable of exhibit- In many ani- 

 ing a continued pulsation, even when perfectly empty and "^^'sp^rtofthe 

 separated from the heart; but this property is limited to a of pulsation, 

 small part of the artery only, which is obviously capable of 

 being essentially useful in propelling the blood, when the 

 ralves of the aorta are closed. The muscular power of the Muscularpow- 



termination of the vena cava is also capable of assisting the ^^°f ^h^endof 

 „,,,,. , -IT. ,7 . '"^ vena cava, 



passage ot the blood mto the auricle. It is not at all im- 

 probable, that a muscle of involuntary motion, which had 

 been affected throughout the whole period of life by alter- 

 nate contractions and relaxations, might retain from habit 

 the tendency to such contractions, even without the neces- 

 sity of supposing, that the habit was originally formed for 

 a purpose to be obtained by the immediate exertion of the 

 muscular power : but in f;ict the partial pulsation of the Use of its par 

 vena cava is perfectly well calculated to promote the tem-''**P*^**''*"' 

 porary repletion of the auricle, while it must retard, for a 

 moment, the column which is approaching, at a time that it 

 could, not be received. 



There is no difficulty in imagining what services the mus- Services to 



cular coats of the arteries may be capable of performing, ^^i^h the 



. , •! • 1 • •• . musuar coats 



without attributing to them any immediate concern in sup- of the arterie,* 



porting the circulation. For since the quantity of blood in "^ ad*pted. 

 the system is on many accounts perpetually varying, there 

 must be some means of arcommodating the blood vessels to 

 their contents. This circumstance was very evident in 

 spme of Hales's experiments, when, after a certain quan« 

 tity of blood had been taken away, the height of the co- 

 lumn, which measured the tension of the vessels, frequently 

 varied in an irregular manner, before it became stationary 

 at a height proportional to the remaining permanent ten- 

 sion, Haller also relates, that he has frequently seen the 

 ^teries completely empty, although in some of his obser- 

 vations there was probably only a want of red globules in 

 the blood which was flowing through them. Such altera- 

 tions in the capacity of the different parts of the body are 

 ahnost always to be attributed to the exertion of a muscu- 

 lar power. A partial contraction of the coats of the smaller 

 I 2 arteries 



