91 



.of the manifest influence of the motions of the brain, on the course of 

 the blood in its veins, and in thesinuses of the dura mater. This experi- 

 ment had been already performed by other anatomists, and amongst 

 others, byRuysch, with a view of proving the immediate communication 

 between the arteries and veins. This communication, which is, at pre- 

 sent, universally acknowledged, may be proved by other facts. This one 

 is evidently any thing but conclusive. 



G. In a trepanned dog, I tied successively the two carotids. The 

 motions of the brain abated, but did not cease. The anastomoses of the 

 vertebrals, with the branches of the. carotids, account for this pheno- 

 menon. 



H. I took a rabbit, a gentle creature, easy to confine, and very well 

 adapted for difficult experiments : after laying bare the brain, and ob- 

 serving that its motions were simultaneous to the beats of the heart, I 

 tied the trunk of the ascending aorta : the moment the blood ceased ris- 

 ing to the head, the brain ceased moving, and the animal died. 



I. The tying of the internal jugular veins, did not stop the motions of 

 the brain ; but its veins dilated, and its surface, bared by the removal of 

 the flap of the dura mater, was sensibly redder than in the natural state. 

 The dog became affected with stupor, and expired in convulsions. 



The opening of these veins did not hinder the continuance of the mo- 

 tions 5 they grew fainter only when the animal was weakened by loss of 

 blood. 



K. The opening of the superior longitudinal sinus, the only one that 

 could easily be opened, did not weaken the motions of the brain. It is 

 observed that the blood flows out more freely from it, during the eleva- 

 tion. 



D. The compression of the thorax, on human bodies, produces but 

 a slight reflux in the jugular veins, especially, if, during this compres- 

 sion, the trunk is kept raised. The reflux is greater, when the trunk is 

 laid flat. 



These experiments might be varied and multiplied ; if, for instance, 

 the injection were thrown, at once, along the vertebral arteries, and the 

 internal carotids ; but those I have stated are sufficient for my purpose. 



Since the first publication of this inquiry, in the Memoirs of the Me- 

 dical Society,* I have had many opportunities of repeating the observa- 

 tions and experiments, which serve as a foundation to the theory there 

 detailed. Among the facts which confirm this theory, there is one that 

 appears to me worth stating: it would be sufficient by itself, if it were 

 possible to establish a theory on the observation of a single fact. A 

 woman, about fifty years of age, had an extensive carious affection of the 

 skull; the left parietal bone was destroyed, in the greatest part of its ex- 

 tent, and left uncovered a very considerable portion of the dura mater. 

 Nothing was easier than to ascertain the existence of a complete corres- 

 pondence, between the motions of the brain and the beats of the pulse. 

 I desired the patient to cough, to suspend her respiration suddenly, the 

 motions continued in the same relation to ea^n other; when she coughed, 

 the head was shaken, and the general concussion, in which the brain par- 



* Memoirs de la Societe Medicale dc Paris, an VII. (1799.) troisieme anne, page 197J 

 ct suiv. 



