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



Time of Proportionate 



Experiment. Compression. recoil. B. P. 



4a .... 1 minute .... 1/T8 .... 125mm. 



6a .... 1 .... 1/1-8 .... 105 



7a ... 30 seconds 1/1-9 110 



8a .... 30 ... 1/2-2 .... 150 



9a .... 30 .... 1/2 .... 105 



12a 4 1/1-2 140 



14a .... 2 .... 1/1-14 .... 125 



20a 2 ,, 1/2 120 



The most noticeable of these is Experiment 8a, in which, although 

 the pressure was comparatively very high, the reaction was almost at 

 its minimum. 



It is clear, then, that the recovery of the volume of the brain is not 

 due to the pressure at which it is irrigated with blood. 



Though these facts appeared to be thoroughly demonstrative, I 

 established a number of control observations to further test the 

 question. 



The first method which suggested itself was naturally that of 

 lowering the blood pressure very markedly by bleeding. This pro- 

 cedure, however, of necessity involves the measurement of the recoil of 

 the brain thus rendered anaemic being taken from a preparation which 

 had already been compressed once ; this, of course, introduces an 

 error, and hence the further question has to be considered how far 

 does one compression experiment have an influence on a consecutive 

 one. 



When compression has lasted for thirty seconds or more it is 

 obviously necessary to allow a sufficient interval to elapse to allow the 

 damaged brain fairly to recover such an interval as half to three- 

 quarters of an hour, sometimes more ; that is to say, I waited till the 

 surface had regained its normal level. Sometimes it is impossible to 

 wait for complete recovery, and, of course, in such a case an element 

 of error is introduced ; but when the time of compression is short, 

 ten minutes is quite enough to allow so as to avoid any appreciable 

 vitiation, of which fact I have satisfied myself experimentally. 



(b.) Comparison of Experiments performed on the same Brain before 

 and after lowering the Blood Pressure by bleeding. After an experi- 

 ment, conducted as above described at normal blood pressure, I bled 

 the animal from the carotid artery. 



As a rule, a large loss may occur without much fall of pressure, 

 and the fall, when it does occur, takes place very suddenly. If the 

 splanchnics be previously divided, the fall takes place earlier and 

 more regularly. Usually I bled to the extent of 150 to 300 c.c. 



By this means there could be produced an enormous fall of blood 

 pressure, sometimes as much as 100 mm. {e.g., from a normal pres- 



