32 PLYMOUTH INSTITUTION. 



November 12th, — Ma. Swaik's Lecture on Circulation. 



Mr. Swain first spoke of the support of organic creatures by the 

 circulation of vital fluids, and mentioned some curious facts res- 

 pecting the circulation in certain plants : he produced a diagram, 

 showing the uninterrupted circle formed by the passages of the 

 fluids of the stone-wort, &c. 



He next shortly adverted to the diff^usion of fluids through in- 

 sects, in which, he said, it was generally supposed that there 

 was no positive circulation, though of late the discovery of struc- 

 tures in their vessels, resembling valves, had thrown some doubt 

 on the correctness of the opinion. 



Mr. Swain then described the heart and vessels of the frog and 

 of fishes generally ; and proceeded with the apparatus found in a 

 man and the mammalia in general, for the diffusion of their vital 

 fluids. 



Mr. Swain spoke of the constitution of the human blood; — 

 and stated that in a certain sense it was to be considered as poss- 

 essed of Vitality. It had been regarded by some, as endowed 

 by a distinct and separate existence, but this was noi the case. 

 It only possessed life in common with the general system of the 

 animal in which it circulated ; when wrthdrawn from that 

 animal, it still retained for a time a degree of vitality, in conse- 

 quence of which, its coagulation took place. The end answered 

 by the coagulation of the blood was, the filling up the openings 

 of the divided blood-vessels; thus preventing a hemorrhage that 

 would destroy life. 



Mr. S. then adverted to the exciting cause of the circulation, he 

 said that it chiefly depended on the muscularities of the heart, 

 and its innate power of contraction ; the propulsion of the blood 

 was however aided by the pressure of the atmosphere on the 

 surface, driving the blood into the temporary vacuum produced 

 by each dilation of the cavities of the heart. 



Mr. S. concluded his lecture by observing, that matter was 

 never attest in our bodies, that old particles were displaced, and 

 new ones substituted. We were perpetually the subjects of 

 change, and, while identity of form remained, the substance of 

 our bodies was never stationary. It was by the agency of circu- 

 lation, that these changes were principally effected, and they 

 might continue without disturbance, for four-score years, when 

 the machine, by which they were directed became worn out and 

 feeble, and at length fell a prey to the chemical influences of the 

 universe, which vitality alone could counteract. 



