292 



took, might have been mistaken by a prejudiced observer, for the proper 

 motions of that organ, and depending on the reflux of blood in the veins* 



In experiments on dogs, the same motion takes place, when the animal 

 barks, but it is easy to perceive, that the concussion affecting the brain is 

 experienced by the whole body, and that the effort of expiration, in bark- 

 ing, causes a concussion more or less violent. 



The patient, mentioned in the preceding observation, died about a 

 month after I came to the Hospital of St. Louis, in which she had been 

 for a considerable length of time. On opening the body, the left lobe of 

 the brain was found softened and in a kind of putrid state; the ichor which 

 ivas formed, in considerable quantity, flowed outwardly, by a fistulous 

 opening in the dura ir.ater whose tissue was rather thickened. 



CLI. The slight consistence of the brain, which Lorry considers as 

 favourable to the communication of the motion which its arteries impart 

 to it, appears to me to be against this transmission. In fact, the dilated 

 vessels not being able to depress the base of the skull on which they rest, 

 make their effort against the cerebral mass, and raise it the more easily 

 (the arch of the skull being removed) from its presenting a certain re- 

 sistance. If the brain were too soft, the artery would merely swell into 

 it, and would not lift it. To satisfy one's self of this truth, one need only 

 observe what happens when the posterior part of the knee rests on a pil- 

 low, or on any thing of the same sort; then, the motions which the pop- 

 liteal artery impresses on the limb, are but little apparent ; but they be- 

 come very visible, if the ham rests on any thing that resists the action on 

 the other knee, for in stance : - then the artery which cannot depress it, 

 exerts its whole action in raising the lower extremity: which it does, the 

 more easily, from acting against a bony, resisting, and hard part. This 

 experiment completely invalidates the opinion of Lorry. The want of 

 analogy will not be objected ; it will not be said that the brain is heavier 

 than the lower extremity, nor that the sum of the calibres of the internal 

 carotid and the vertebral arteries, is not greater than that of the popliteal 

 artery. 



This continual tendency of the brain to rise, produces in the end, on 

 the bones of the skull which resist this motion, very marked effects. 

 Thus, the interior surface of these bones, smooth, in early life, becomes 

 furrowed with depressions, the deeper as we advance in aqe. The digi- 

 tal depressions and the mammillary processss, corresponding to the con- 

 volutions and windings of the brain, are very evidently the result of its 

 action on the enclosing parietes. Sometimes it happens, that, at a very 

 advanced age, the bones of the skull are so thinned by this internal ac- 

 tion, that the pulsations of the brain become perceptible through the 

 hairy scalp. 



No doubt, the same cause hastens the destruction of the skull by the 

 fungous tumours of the dura mater. The effort from expansion of the 

 tumour, which develops itself, is further added, and makes the waste of 

 the bones more rapid. At the end of a few months, the tumour projects 

 outwardly, with pulsations plainly simultaneous to the beadnga of the 

 pulse, as Louis observes in a Memoir inserted among those of the Aca- 

 demy of Surgery. 



1 have shown (CXLIX.) that the opposition of the veins of the brain 

 and of the sinuses of the dura mater w<xs adverse to the action ascribed 

 to them, on this viscus. Experiment (E. L.) shows that the stagnation 



