Brain ami the Conditions of Recovery after Compression. 5 



ported in the usual holder. The skull was exposed on one side, and the 

 median and fronto-temporal ridges chiselled away as far as necessary, 

 BO as to give a flat surface for inserting the screws. The skull was 

 trephined close to, but carefully avoiding, the longitudinal sinus. 1 

 found haemorrhage a very troublesome accident, and that it was 

 essential to stop it by means of wax and amadou before proceeding 

 with the experiment, as the presence of even a thin layer of blood on 

 the cortex marred the result. The object of applying the compression 

 as near as possible to the middle line was to arrange the line of pressure 

 perpendicularly downwards, so as to avoid any elastic reaction from 

 the falx cerebri ; this seemed to be more important in using large 

 weights, which evoke larger excursions. I enlarged the opening in 

 the skull with bone forceps, so as to allow of easy insertion of 

 the plunger, and give sufficient margin to observe the condition of 

 the brain surface. The next step was to reflect the dura rrmter, insert 

 the screws (using a guarded bradawl to make preliminary holes), and 

 then to erect the apparatus so that the disc of the plunger rested flat 

 on the surface of the brain, and the plunger itself was absolutely 

 perpendicular. 



The blood pressure was recorded by means of a mercurial mano- 

 meter connected with the femoral artery. The respirations were 

 traced by means of a Paul Bert receiver and a Marey recording 

 tambour. 



In performing an experiment I noted the moment of applying the 

 weight to the pan, and then recorded the figures the index pointed to 

 at intervals of so many seconds during and after compression, and 

 also read off the blood pressure at stated intervals. 



5. Considerations Affecting the Plan of Experiments. A few remarks 

 on special conditions observed during my experiments may now be 

 briefly noted. 



(a.) Various conditions of the cranium and its contents, affecting 

 the apparent elasticity of the brain, and requiring attention, are 

 as follows : 



Adhesions of the pia mater to the dura mater, as, for instance, by 

 vessels running from one to the other. 



The Falx Cerebri. This is not large as a rule in the dog, often not 

 more than 5 or 6 mm. broad in a small dog, and is not likely to have 

 much influence, but large weights applied in a direction fairly per- 

 pendicularly to its surface might reasonably be expected to be 

 limited in effect by its elasticity. 



The Tentorium. This is generally almost totally ossified in dogs, 

 but in some dogs there exists sufficient membrane to prove a factor 

 in causing some elastic reaction from the base of the skull. 



The Shape of the Cranium. It seems probable that the vertical 

 depth of the skull cavity should modify results somewhat, as with a 



