Circulation of the Blood. 187 



siderable lapse of time. And now, assuming the doctrine 

 which I am advancing to be true, there are very obvious rea- 

 sons that the blood, so long as it moves in the system, has its 

 tendency to coagulate satisfied in a very partial manner. Let 

 us observe its course. It leaves the left ventricle of the heart, 

 one pulse-wave succeeding another with rapidity, and is dis- 

 tributed through all the aortic branches. It takes but a few 

 seconds for this movement to be complete, a period far too 

 short to allow coagulation to take place ; it now passes on 

 through the capillaries, or moves through parenchymatous 

 structures ; and here, even though a great delay may occur, 

 inasmuch as the passages are so sinuous and often so minute 

 that the discs can move but in a single file at a time, how is 

 it likely, under such circumstances, that coagulation should 

 ensue ? For that to take place, it is needful that there should 

 be a free communication throughout the mass, that each par- 

 ticle of fibrine brought into relation with those around it may 

 exert its plastic power and join itself to them. But in the 

 peripheral circulation it is isolated, the cells over which it is 

 moving, or the narrow tubes through which it goes, protect 

 it from other particles around, and on escaping into the com- 

 mencement of the venous trunks, it is hurried in the torrent 

 of the circulation at once to the heart. Without delay the 

 right auricle and ventricle pass it forward to the lungs, and if 

 any tendency to set had been exhibited during the brief mo- 

 ment of its passage, it is again distributed upon the capillaries 

 of the lungs, and is situated precisely as it was when in the 

 capillaries of the peripheral system. 



In this manner I regard the coagulation of blood as a sim- 

 ple mechanical result, having no connexion with life or death, 

 or the fictitious principle of vitality. At the two extremes of 

 the circulation, the peripheral and the pulmonary, there is a 

 sorting process continually going on. If a man were to agi- 

 tate a quantity of this liquid in a tube, having a contrivance 

 at each extremity to keep the particles of fibrine as they passed 

 apart from one another, their plastic tendency to cohere could 

 never be satisfied, and coagulation could never ensue. And 

 this condition of things is, to a certain extent, approximated 

 to in the mechanism of the body. 



It thus appears that by the intervention of two capillary 

 circulations, one in the lungs and the other in the system, the 

 coagulation of blood must be greatly retarded, though the 

 tendency to produce that result is quite as great as when the 

 fluid is removed from the system. And with such an obvious 

 explanation before us, why should we resort to any occult 

 agency, or envelope the phaenomenon in mystery, when it is 

 plainly a mechanical affair ? 



