28 THE TONER LECTURES. 



are particularly dangerous in those Avliose vessels are atheromatous 

 or otherwise diseased from age or special cause. Over-work of the 

 brain, for a time, at least, flushes it with blood and distends its 

 vessels. Even a pure intellectual act can be shown to notably in- 

 fluence the circulation, and change the temperature of the head. 



GkV has studied the influence of the intellectual act upon the 

 circulation. He used a cardiograj^hic tambour on his own carotid. 

 A philosophical lecture, a geometric demonstration, and an arith- 

 metical operation were used to excite the activity of the brain. He 

 observed during the intellectual work, 1, augmentation of the 

 number of beats of the heart, which ai:)peared to be in direct ratio 

 to the attention ; 2, dilatation of the carotid artery and most 

 marked dicrotism of the carotid pulse ; 3, these characteristics per- 

 sisted after cerebral activity had ceased. He concluded that these 

 effects were neither cardiac nor respiratory, but vaso-motor changes. 



The experiments of Lombard on the effects of mental activity 

 in increasing cerebral temperature are now well known. 



Frequent congestions of the Ijrain cause j^eculiar kinkings and 

 tortuosities of the arteries, even of those of large calibre. I have 

 seen many remarkable examples of this condition in the post- 

 mortem room of the Philadelphia Hospital. The fact that the peri- 

 vascular spaces in the brain allow these kinkings to take jjlace is, to 

 a certain extent, conservative of the coats of the vessels ; but, in pro- 

 cess of time, the arterial tunics will degenerate as the result of the 

 strain to which they are frequently subjected. We speak some- 

 times of cerebral centres and zones, referring to collections of 

 nerve-cells which are supposed to have certain special functions ; 

 but centres and zones are vascular as well as nervous. Instead 

 of innervation preceding circulation, or circulation innervation, 

 the two practically go hand in hand in l^rain activity. An 

 area of blood supply was regarded by Laycock^ as indicative of an 



1 Kevue des Sciences 31edicales, quoted in the Journal of Xervous and 

 Mental Disease for April, 1882. 



2 Medical Times and Gazette, August 10, 1871. 



