165 



so contradictory, that one is surprised that so judicious a physiologist 

 should have collected them to establish a theory completely refuted by 

 several of them. Nothing, for example, contradicts it more fully, than 

 the continuation of the flow of the blood, in the vessels of frogs and sa- 

 lamanders, after the hearts of these reptiles have been torn out: there 

 are, besides, animals which, not possessed of that central organ, have 

 nevertheless, vessels along which the blood flows, and which contract 

 and dilate, by alternate motions. 



If the mere force of the heart propelled the blood to every part, the 

 course of this fluid ought, at intervals, to be suspended, its circulation, 

 at least, ought to be slackened, when the ventricles cease to contract; 

 but as the contraction of the arteries corresponds to the relaxation of the 

 ventricles, these two powers, whose action alternates, are continually 

 employed in propelling the blood along its innumerable channels. 



Besides the general circulation, of which the laws and phenomena 

 have just been mentioned, each part may be said to have its peculiar 

 mode of circulation, more or less rapid, according to the arrangement 

 and structure of its vessels. Each of these individual circulations forms 

 a part of the machinery included in the great circle of the general circu- 

 lation, and in which the course of the blood takes place in a different 

 manner, may be accelerated or retarded, without affecting the general 

 circulation. Thus, in a whitlow of a finger, the radial artery pulsates 

 a hundred times in a minute, while on the sound side, its beats are only 

 seventy in number, and perfectly isochronous with the pulsations of the 

 heart*. In the same manner, the blood of the intestines, which is des- 

 tined to furnish the materials of bile, flows much more slowly than that 

 of other parts. 



These modifications affecting the velocity of the circulatory motion of 

 the blood, account for the difference of its qualities in different organs; 

 all these differences form a part of the plan of nature, and it is not difficult 

 to understand their utility. 



LXVIII. In what has been said of the circulation, no separate mention 

 has been made of the course of the blood through the lungs, called by 

 authors the lesser or pulmonary circulation. The vascular system of the 

 lungs, with the addition even of the cavities of the heart which belong to 

 it, does not represent a complete circle, it is only a segment, or rather 

 an arch of the great circle of general Circulation. 



The blood, in going along that great circle, meets with the organs, 

 situated like so many points of intersection in the course of the vessel 

 which form that circle. 



To render still more simple, the idea which is to be entertained on the 

 subject, one may reduce these intersections to two principal ones; the 

 one corresponding to the lungs, the other to the rest of the body; the 

 veins, the right cavities of the heart, and the pulmonary artery with its 



* This assertion is altogether too roundly made, and appears rather to be one of 

 those things which are received as true from having been often repeated, than the ac- 

 curate detail of a well observed fact. That there may be a difference in the degree of 

 dilatation and force of pulsation in different arteries is well known, and may depend on 

 the peculiar condition of the nerves supplying the affected vessels, but that one radial 

 artery should beat one hundred strokes in "a minute, while the other beats but seventy* 

 presupposes the existence of a power in the arteries themselves which has never yet 

 been fnwed, however often it may have been supposed. Godmafi, 



