293 



of the blood, or even its regurgitation, could produce only a slow and 

 gradual distension of the sinuses of the dura mater, and veins terminating 

 in it, with a slight turgescence of the cerebral mass, if the cause, pro- 

 ducing the stagnation of the blood or its reflux, prolonged its action to a 

 partial destruction of the skull. 



Lastly, the alternate motions of the brain, said to correspond to those 

 of respiration, ought to be the beats of the pulse, in the ordinary ratio of 

 1 to 5. On the contrary, it is easy to satisfy one's self that these mo- 

 tions are in an inverse ratio, and perfectly simultaneous to the pulsations 

 of the heart and arteries. 



Theresults of the experiments I have stated in that Memoir, compared 

 to those obtained by justly celebrated inquirers, are too remarkably dif- 

 ferent not to have induced me to make some attempt at investigating the 

 cause of our disagreement. For that purpose, I thought it necessary to 

 examine scrupulously all the circumstances. 



The work of Lamure contains anatomical errors, which throw suspi- 

 cions upon his accuracy. Haller did not himself make the experiments 

 of which he speaks, in treating of the influence of respiration on the cir- 

 culation of venous blood. This article is drawn from a thesis defended 

 at Gottingen by one of his disciples. Lastly, Vicq-d'Azyr attempted no 

 confirming experiment, and seems to have had in view only the reconcil- 

 ing all opinions. 



No one of those anatomists has distinguished the motions of elevation 

 impressed on the cerebral mass by the influence of its arteries, from the 

 swelling of the sinuses of the dura mater, of the veins distributed to it, 

 and from the tumefaction of the brain which may be caused by difficult 

 respiration. This mistake would be the more easy, as animals tortured 

 by the knife of the anatomist, breathe painfully, convulsively, and at 

 shorter intervals than in their natural state. Schlitting, the first author 

 of these experiments, appears especially to have confounded the motion 

 of rising, the real displacement of the brain, with the turgescence of this 

 viscus. At every expiration, he says, I have seen ths brain rise, that is 

 to say, swell, and at every inspiration I have seen it fall, that is to say, 

 collapse. 



"Toties animadverti persfiicue in omni exfiiralione, cerebrum univer sum 

 ascendere, id est intumescere ; atque in quavis inspiratione iliud descendere, id 

 est detumescere." 



We may, therefore, consider as a truth strictly demonstrated by obser- 

 vation, experiment, and reasoning, the following proposition : 



The motions observable in the brain, when laid bare, are imparted to it solely 

 by the pulsations of the arteries at its base, and are perfectly simultaneous to 

 the fiulsations of these vessels : further, the reflux and stagnation of the venous 

 blood* are able to swell its substance. 



CLII. fiction of the nerves and brain. It is undoubtedly, as Vicq-d'Azyr 

 has said, by a motion of some sort that the nerves act. ' Setting out from 

 this simple, idea, one may admit several kinds of nervous motions, the 

 one operating from the circumference to the centre, it is the motion of 

 sensation which we are about more particularly to study in this para- 

 graph ; the other, acting from the centre to the circumference, and this 

 motion, produced by the will, determines the actitfn of the muscular or- 

 gans, &c. 



In what manner arc the impressions produced on the senses by the bo- 

 dies which surround us, transmitted, along the nerves to the brain ? Is it 



