34 Mr. Martyn Roberts on the Analogy between the 



ries, capillaries, and veins of a dead body ; this pressure, on a 

 syringe of one and a half inch in diameter, would be about 

 four pounds ; and surely every one will allow that a force of 

 four pounds thus applied would be insufficient to inject the 

 whole body, even with a liquid much less viscid and adherent 

 than blood, and if not sufficient to inject it, how much less to 

 impel such a circulation throughout the system as is main- 

 tained in the living being ! 



12. That the heart derives no assistance from the arteries 

 in propelling the blood, may be proved from the structure of 

 these vessels. To possess a propulsive power they must have 

 muscular contractility ; mere elasticity of tissue endows them 

 with no force; it simply causes them to act as regulators to 

 the flow of blood impelled in waves by the rhythmic action of 

 the heart ; the air chamber in the fire engine is a similar re- 

 gulator to the jet of water, compensating for the periodic in- 

 jections of the pumps ; the elasticity of the arteries causes a 

 continuous flow of blood through the capillaries, but cannot 

 force it onwards. It has been fully proved by Miiller, Ber- 

 zelius, Hodgkin and others, that the coats of the arteries are 

 not muscular; and I need not enter into arguments deduced 

 from experiment on their non-muscularity, for I believe this 

 is now the generally acknowledged structure of the arterial 

 coats, and that they possess no more muscular action than so 

 many India-rubber pipes, having but elasticity, which re- 

 mains long after death, indeed, until decomposition com- 

 mences. 



13. We may then rest satisfied that the arteries in no mea- 

 sure assist the heart to propel the blood, neither can the veins 

 to any considerable amount; and we are therefore driven to 

 the necessity of acknowledging that as the heart's force is in- 

 sufficient to overcome the adhesion between the blood and the 

 parietes of the capillaries, there must be some power destroy- 

 ing this adhesion, and thus allowing the heart to maintain a 

 free circulation throughout the whole system. 



14. This power destroying the adhesion, I hold to be the 

 neuro-electric action. I have already shown that electricity 

 suffices for a like purpose in inorganic bodies, and physiolo- 

 gical facts prove the circulation in the capillaries to be greatly, 

 if not altogether influenced by the nerves, which are undoubt- 

 edly the sources of the neuro-electric power. 



15. The first of these facts is, that the smaller the diameter 

 of the capillaries, the greater is the proportion of nerves distri- 

 buted upon them, this being necessary to give the larger quan- 

 tity of neuro-electric power requisite to overcome the increased 

 adhesion in these smaller capillaries, caused by the contact of 



