The Harveian oration on advances in knowledge regarding the circulation and attributes of the blood since Harvey's time : delivered before the Royal College of Physicians of London on October 19, 1914 / by Richard Douglas Powell.

Powell, R. Douglas (Richard Douglas), Sir, 1842-1925.

Date:: 1914

Credit: The Harveian oration on advances in knowledge regarding the circulation and attributes of the blood since Harvey's time : delivered before the Royal College of Physicians of London on October 19, 1914 / by Richard Douglas Powell. Source: Wellcome Collection.

Provider: This material has been provided by Royal College of Physicians, London. The original may be consulted at Royal College of Physicians, London.

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$stimulated, contracts at once with its full power and that a stronger stimulus will not have any further effect, differing thus from the graduated force of contraction of skeletal muscle according to strength of stimulus, and the conclusion is drawn that if the heart contract at all its contraction is maximal, “ for all it is worth.” Even if this observation be trustworthy it will not apply to the living heart under vital conditions of innervation. As pointed out in Howell’s “ Text- book of Physiology” (p. 573), “numerous observers have called attention to the fact that the vagus fibres may also cause a weakening in the force of the beat as well as a slowing in the rate, or, indeed, the two effects may be obtained separately.” In no other organ of the body is there a more manifest reserve of functional power to meet the exigencies of varied conditions of effort, of arterial resistance, of emotion, of sudden or gradual valvular defect or other vicissitudes of life. It is to be noted that later observations have disclosed another peculiarity of heart muscle unknown to Bowditch a.t the time of his experi- ments—namely, that at the time of contraction the heart muscle is “ refractoi*y ” to further stimulus. It is possible that this fact may vitiate the con- clusions drawn from electrical stimulation of heart muscle, and I do not know whether it has been allowed for. Effect of Lung Elasticity on the Circulation. In addition to the driving power of the ventricles, roughly recognised as equivalent to 6 and 3 inches Hg respectively, there are certain further aids a tergo to the circulation which may be briefly enumerated. They are partly sustaining and partly supplementary. The driving power is sustained and carried on with least possible loss (1) by the elastic recoil of the great vessels upon their closed valves ; (2) it is said (Lauder Brunton and T. D. Lister) that there is a certain rhythmic or rather peristaltic contraction of the smaller vessels which has some slight effect in propelling the blood through the$