230 Royal Society. 



independently of that circulation. He shows it to be necessary to 

 circulation, that two fluids, or a fluid in two diflferent states, should 

 communicate by two points or extremities with each other, and that 

 these extremities should present such a resistance to their mutual 

 connexion and commixion, that the transfer of conditions of each, 

 from one to the other, must take place, otherwise the uniformity of 

 both would speedily put an end to the process ; and it is indicated 

 that the forces in operation in these two places would be reverse to 

 each other ; in the one it would be from arterial to venous, and in 

 the other from venous to arterial. 



The blood-vessels containing the two kinds of blood are com- 

 pared by the author to two bar- magnets placed side by side, the 

 pulmonary and systemic capillaries representing the armatures placed 

 at their extremities ; with this limitation, that as the changes in 

 the blood take place onlj'' in the two opposed sets of capillaries, 

 the force is necessarily generated only in them, and therefore the 

 intermediate blood contained in the larger blood-vessels merely re- 

 presents conducting wires completing the circuit. The left side of 

 the heart is viewed as being placed in the largest ampulla of the arte- 

 rial circulation, and the right side of the heart as being in the like 

 position with respect to the venous current. 



The portal circulation is alluded to, in order to prove that a pro- 

 pelling force is not essential to produce circulation of blood. An 

 account is given of numerous experiments on various animals, in 

 which the ends of two similar wures (in some cases of copper and in 

 others of platinum) were inserted ; that of the one into a vein, and 

 that of the other into an artery, the free ends of both wires being 

 brought into connexion with a delicate galvanometer ; and it was 

 found that during life a galvanic current was indicated, passing along 

 the artery and returning by the vein ; that this current became more 

 feeble in proportion as the vitality of the animal declined, and again 

 more strong as the effect of the chloroform, which was administered 

 for the purpose of preventing pain, subsided. 



The author also observed, that the strong action of a muscle (the 

 sterno-mastoid) between the two blood-vessels tended to discharge 

 the galvanic force as it was generated ; and that when that muscle 

 was divided, the galvanic force became much stronger. When the 

 connexion of the current with the lungs was severed by a ligature 

 placed on the vein between the insertion of the wire and the heart, 

 the current was instantly reversed, passing up the vein and returning 

 by the artery. The same reverse current was indicated when the 

 wires were inserted into portions of the blood-vessels which had been 

 isolated, each by two ligatures, placed the one above and the other 

 below the insertion of the wires. A similar effect was also obtained, 

 as long as the blood continued to coagulate, when the two kinds of 

 blood were drawn from the blood-vessels into separate cups, and 

 brought into connexion with the galvanometer ; the blood in the cups 

 being connected together Ijy the ends of a piece of copper or of a 

 strip of muscle dipping into each. 



Several experiments are related, tending to prove that the power 



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