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dple of elasticity, the contraction of arteries. But however correct this 

 explanation may be, with regard to the vessels near the heart, it does not 

 apply to the capillaries; the influence of that organ does not operate on 

 these vessels. One may easily conceive, that the column of blood which 

 by the impulse it has received, in the first instance, has been sent along 

 the whole length of tubes whose sides are ossified, inflexible, and conse- 

 quently inert, on reaching the extremity of these canals, is, in a manner, 

 again taken up by the vital power residing in the capillary vessels, and 

 circulates from the influence of the action belonging to these vessels*. 

 Besides, elasticity, however considerable, merely restores those tissues 

 that have been stretched, to the condition in which they were before ex- 

 tension. Elasticity is a kind of re-action, proportionate or relative to the 

 action which precedes it. Why do arteries in the living body contract, 

 to such a degree, that when empty, their canal becomes obliterated, 

 while in the dead body, however perfect the depletion of the arterial 

 system may have been, the cavity of the arteries remains perfectly open. 

 Several physiologists, however, and those among- the most modern, con- 

 sider elasticity as the principal cause of the progression of the blood 

 along the arteriesf. 



As the distance from the centre increases the circulation slackens, from 

 several causes, and the blood could not reach all the parts of the body, if 

 the arteries, whose vitality increases with their distance from the heart, 

 and as they become smaller, did not propel it to all the organs. The 

 causes which retard the circulation of the arterial blood, are, the increased 

 dimensions of the space in which it is contained ; the resistance from the 

 curves of the vessels; the friction which it undergoes, and which in- 



* I have dissected the brain of a female, (apparently 1 between fifty and sixty years 

 old,) in which the arteries were rigidly ossified from their great trunks, down to 

 branches not larger than a tine knitting 1 needle. In the left thalamus opticus there was 

 a brownish discolouration, which seemed to m-.irk the spot where blood had been ef- 

 fused some time before death. Godman. 



-j- It has always been a matter of controversy among physiologists, whether the blood 

 is propelled by the heart only, or whether the" arteries co-operate to the same end. It 

 is well known that the illustrious Harvey, the discoverer of the circulation, was of the 

 former opinion, and that he has since been supported by many followers. We admit, 

 at once, that the heart is the chief organ concerned, but it seems to us equally true that 

 the arteries also exercise a considerable agency, most commonly as auxiliary to the heart, 

 yet sometimes to a certain extent independently of that organ. These two positions 

 are demonstrable, both by experiment and fact. 



1. It has been proved that the muscular power is inherent in all the arteries of the 

 body, in the large and small, in the main trunks as well as in the capillary extremities. 



2. That the arteries contract with considerable force, the natural and unavoida- 

 ble effect of which must be, the propulsion of the blood, and the quickening of the 

 circulation. 



3. That the circulation has been maintained in the foetus, though utterly destitute of 

 a heart. Cases of this description are recorded in sufficient number, to put the fact be- 

 yond a doubt. It may, however, be alleged, that in these instances, as very often hap- 

 pens in the history of the animal economy, the want of one organ is supp ied by the as- 

 sumption of new, or increased powers by some other. We do not perceive much force 

 in this objection, but as it might be raised, we will appeal to other facts of a less dis- 

 putable nature, such as are afforded by the phenomena of local inflammation, active 

 haemorrhages, blushing, hectic suffusion, and many more which it would be easy to 

 enumerate. Enough, however, have been mentioned, to show that the circulation may 

 be increased in a particular part without its being generally affected, and consequently 

 that the heart is not the only power which propels the blood, but that this force also 

 resides, in a limited degree, in the arteries. Chapman. 





