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



deep skull a greater depth of brain substance comes directly tinder 

 compression than in the case of a flat sku-ll, but this and the fore- 

 going conditions have but a subsidiary influence upon the effects 

 observed, the main factor which influences the more immediate recoil 

 of the brain surface, in experiments performed upon the organ in 

 situ, being the rigidity of the bony floor it rests upon. 



(6.) Moulding. After a compression of thirty seconds or so there 

 frequently results a faint ringed impression of the disc this usually 

 disappearing in about half an hour. After several experiments have 

 been performed upon the same spot, a considerable saucer-like 

 depression in some cases ensues. 



(c.) (Edema. On several occasions a curious phenomenon was ob- 

 served, which most probably has its origin in local oedema. It is 

 more especially marked in experimenting with small weights, 20 to 

 50 grams, applied for a couple of seconds only. When the weight, 

 after compression, has been removed, and the brain surface, in re- 

 covering, has ceased to push the disc up farther, then if the passively 

 resting disc be removed from the surface, the latter will start a 

 further rise almost immediately, so that in a few minutes it may even 

 be at a higher level than that at which it stood when the ex- 

 periment was started. After more severe compression this is not 

 observed. 



(rf.) Powerful respiratory movements, as will be shown directly, 

 are liable to vitiate results by aiding recovery after compression, 

 through the medium of increased venous pressure. Hence the 

 necessity already mentioned of maintaining a fairly deep narcosis. 



(e.) The direct effect of compression upon the blood pressure and 

 respiration. 



I found that the local compression by any weights that I employed 

 was, in view of the cranium being freely opened, insufficient to 

 produce any effect, either upon the blood pressure or respiration, 

 this being so far fortunate as then could be no indirect influence 

 from this cause upon the elasticity of the brain. The minimum 

 weight which can affect respiration, even slightly, was 200 grams. 



B. Results of Compression Experiments on the uninjured Brain, the 

 Blood Pressure being normal. 



(a.) Definitions. I employ the term " uninjured brain " to denote 

 that no previous experiment has been performed on the same brain ; 

 the effect of previous compression in destroying the value of subse- 

 quent experiments is discussed later. 



The' term "excursion " I have applied to the extent to which the 

 plunger enters into the cranial cavity (by a reason of sinking of the 

 brain) on a weight being applied. Fig. 3 (a&). 



