MEMOIR OF MAGENDIE. 97 



them.* Their action depends on their elasticity, an elasticity which is very 

 decided, hut yet purely physical. The first object of experiments in physiology 

 is the distinction of forces ; M. Magendie already recognized thi.? great aim, and 

 attains it here by a skilful discrimination. The circulation of the blood com- 

 mences through the contractility of the heart, a vital force, and is continued 

 through the elasticity of the arteries, a physical force. 



It is well known by how profound an aversion for all conjecture, by how 

 exact an observation of facts, the researches of ]\I. de Laplace were marked, and 

 how much they contributed to maintain in the academy the severe spirit of the 

 experimental method. Laplace desired that all science should be but an assem- 

 blage of facts rigorously concatenated ; and after having, according to the feli- 

 citous expression of M. Cuvier, suhjectcd the heavens to geometry, ho did not 

 despair probably of establishing the same order of things upon earth. The 

 decisive and absolute manner in which the young physiologist was accustomed 

 to draw his conclusions, not always safe, however, from subsequent retraction, 

 appeared to Laplace w(ll suited to the style of a geometer. And if it be an 

 essential quality of the latter to yield deference to no one, few certainly could, 

 in this respect, be better qualified for the function than our colleague. 



M. Magendie, confident in his own strength, held himself aloof with a dis- 

 dainful pride, eluding every ordinary encouragement. But it came to pass that 

 one day the illustrious, the rigid, the judicious Marquis de Laplace volunteered 

 the first advances towards him. Electricity is less potent, for this acts not on the 

 spirit, than are the few words of encouragement which fall from the lips of a 

 great man. Our sceptic thought himself secure from all enthusiasm, and was 

 only the more hurried away by it. It was not long after this that M. de Laplace 

 said to his old friend M. de Montyon : " It is greatly to be regretted that learned 



* The conclusions at which lie arrived are: " 1st, that the arteries, great .ind small, pre- 

 sent no trace of irritability.^' This we now know to bo too absolute; the arteries, especially 

 the small ones, are irritable. This does not hinder, however, their function in the circula- 

 tion from being principally due, as Magendie saj's, to their tlasticity — to the elasticity of 

 their middle membrane, then* yellow tissue. "2dly: that the contraction of the lelt ventricle 

 and the elasticity of the arteries supply a sufficient mechanical reason for the movement of 

 the blood in these vessels." (Magendie, Journal de physiologie crpcrimentale, t. I, p. 114.) 



Long afterwards, in one of his best lectures at the college of Fiance, he recurred to tho 

 part borne by the elasticity of the arteries in the circulation, and with a development well 

 worth remarking: "The part which elasticity bears in the great act of circulation is too im- 

 portant not to detain us ibr a moment. The heart — a centnil organ which may be compared 

 to an hydraulic pump — is intended to force continually, but by alternating impulsions, blood 

 into the system of tubes, wiiichgoes on subdividing itself, and constitutes what we call arte- 

 ries. These become reduced into extremely slender ducts which, under the name of capillary 

 vessels, proceed to inosculate with another system of tubes — the veins — which convey the 

 blood back from the periphery to the common centre whence it flowed. Such, on a large 

 scale, is the phenomenon of circulation. It is readily conceived that the contraction of the 

 left A'entricle may be siiliiiciently .energetic to drive the liquid into the arterial system, but is 

 its action propagated even into the capillary and venous conduits? This problem must now 

 be resolved in the affirmative." [8ee on this point the re.'^earches of M. Poiscuiile, one of 

 his pupils, whom Magendie regarded as doing him most honor.] " A first phenomenon is 

 this: the heart, each time that, it contracts, throws into the arterial system a wave of blOod, 

 and as each contraction is alternate, it follows that the blood must be projected by inter- 

 rupted jets. This consequence is plain; yet observe now what passes in the vessels where 

 it circulates. If we open an artery near the heart the blood escapes in distinct jets; if the 

 vessel is distant from the heart the flow is unil'orm and continuous ; and if we open finally 

 one of the small arterial ramifications which form the capillary nit-work, the blood spreads 

 itself uniformly in a sheet. How comes it that an alternating prcssttre, like that of the con- 

 traction of the ventricle, can in the end produce a continuous efflux? By what process of 

 nature is this remarkable result accomplished ? I]y the elasticity of tho walls of the arterial 

 vessels. If I be not mistaken, I was myself the first to insist on this wholly mechanical 

 explanation, the only one which renders an exact accoimt of this singular phenomenon. In 

 effect, the jet of blood which the ventricle projects into the aorta makes itself felt in all tho 

 arteries Avhose walls it distends; the impulsion ceases, but the sanguineous current is not on 

 that account interrupted, for these walls contract upon themselves in virtue of their elastic 

 property, and exert on the contained liquid an energetic compression." (Leqons sur ies 

 ph^nomencs physiques de la vie, t. I, p 171-183.'' 

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