1894.] Elasticity of the Living J3rain, c. 277 



assure. A compression by a 50-gram weight for a period of from 

 ) seconds to one minute yields an average proportionate recoil of \. 

 further comparison definitely shows that the longer the period of 

 compression the less is the recoil ; thus with a compression of only 

 two seconds the reaction is sometimes almost perfect, whereas a 

 compression lasting six miuutes yields a ratio of 1/2* 74. Heavier 

 weights similarly damage the brain in a fashion -prejudicial to its 

 recovery. 



A series of experiments were performed with a view to comparing 

 the " elasticity " of the brain at the normal blood pressure with the 

 " elasticity " of the same brain at an artificially lowered blood pressure. 

 The first method employed was that of producing a large fall of 

 blood pressure by bleeding. The results tended to confirm the im- 

 pression that there exists no constant relation between brain elasticity 

 and blood pressure. This series is somewhat vitiated by the partial 

 collapse of the cerebrum which ensues during the process of bleeding, 

 ,nd a second series was instituted, in which the blood pressure was 

 wered through the agency of amyl nitrite; the brain at the moment 

 administration becoming flushed with blood, it has no tendency to 

 llapse. Under the influence of this drug the cerebral vascular con- 

 itions are such that the " elasticity " is actually increased, thus con- 

 clusively demonstrating the non-dependence of the latter upon the 

 central arterial pressure. 



A further series of experiments were performed in view of the 

 fluence which venous pressure is believed to exert upon the cerebral 

 :ulation. This object was carried out by exposing the accessible 

 anial veins and clamping them in succession, and by measuring the 

 .riation in the intra-cranial pressure induced by this means. The 

 suits tended to show that the increase of intra-cranial pressure 

 must be considerable to influence the "elasticity" in even a small 

 degree. 



Experiments performed upon brains which had undergone pro- 

 >nged or severe compression showed that a considerable increase 

 f arterial blood pressure is quite unable to restore the volume of the 

 >rain thus damaged, whereas an increase of venous pressure, obtained 

 y asphyxiation, rapidly, and usually completely, brings this about. 



