2 Mr. A. G. Levy. On the Elasticity of the Living 



physical properties of the brain substance, and deductions drawn 

 from my observations must not be immediately applied to explain the 

 changes in the brain seen in cases of meningeal haemorrhage, tumours, 

 &c., because, in order to ascertain the fundamental facts, the experi- 

 ments in the present case have of necessity been made with the 

 cranial cavity open, the dura mater partially reflected, and a certain 

 quantity of the cerebro-spinal fluid consequently drained away. In 

 pathological conditions the pressure is exerted in a closed, fluid-con- 

 taining cavity, and hence any local compression must evoke a reac- 

 tion from all parts of the cerebral environments, and all parts of the 

 intracranial contents are at an equally exaggerated pressure. In my 

 experiments, the cranial cavity being opened, the influence of the 

 cranial walls is limited, and the pressure is directly exerted upon, and 

 principally confined to, the part of the surface compressed and the 

 mass below it. 



I may mention that I started with the generally accepted premise 

 that the elasticity of the brain is more or less proportional to the 

 central blood pressure, and many of my earlier experiments were per- 

 formed with the object of testing what at first sight seems an exceed- 

 ingly reasonable view. 



2. Historical Introduction. I have throughout my experiments 

 taken as an indisputable fact what was demonstrated by Grashey,* 

 viz., that the cerebral tissue itself is practically incompressible (in 

 fact, its coefficient of compressibility being rather less than that of 

 water), and that any reduction in volume of the living brain must 

 therefore be due to the squeezing out from its blood vessels, lympha- 

 tics, and ventricles, of blood, lymph, and cerebro-spinal fluid. 



Grashey's experiments consisted of a careful estimation of the com- 

 pressibility of the dead brain by hydraulic pressure in a delicate 

 piezometer. His experiments conclusively showed what had indeed 

 been the general teaching, but he was led to make this demonstration 

 by reason of the extraordinary assertion of Adamkiewiczf that the 

 brain tissue itself bears the brunt of the diminution of the intracranial 

 space. 



The records 1 on compression of the brain substance are numerous, 

 and the methods employed by the investigators (Cooper, Duret, 

 Kahler, Pick, Leyden, Adamkiewicz, Spencer and Horsley, Dean, 

 Hill, &c.) are very various ; but these experiments have been arranged 

 from the clinical point of view, i.e., the effect of compression upon 

 the functional activity of the nerve centres. 



Some observers have noted the structural changes produced ; thus, 



* Grrashey, " Ueber Hirndruck und Hirncompression," 'Allg. Zfcschr. f . Psychiat.,' 

 Berlin, 1887, 43. 



t Adarakiewicz, "Die Lehre von Hirndruck und die Pathologic der Hirn- 

 compression," ' Sitznngsberichte d. K. Akademie, Wien,' Band 88, 1883. 



