56 On fittra- Cranial Pressure. [Jan. 25, 



a lasting rise of intra-cranial pressure and physiological effect*. 

 These are the same as in the cat, except that there is no rise of blood 

 pressure. 



20. On cutting both vagi iu the dog, the rise of blood pressure 

 occurs as in the cat, and may reach enormous amounts. 



21. The compensation is reduced to nothing in the dog on repeating 

 the experiment a second time, and the effects are much more severe. 



22. The physiological effects can be immediately removed by 

 emptying the bag, and the pressure in the intra-cranial cavity 

 recovers its old standard. 



23. If the displacement caused by the bag is large, and maintained 

 for a considerable time, there may be no relief and no expansion of 

 the brain on emptying the bag. 



24. Trephine holes made in various parts of the cranium and 

 vertebral column afford no relief to the effects produced by the bag. 



25. No fluid is to be found within the subdural space after the 

 " bag experiment." The surface of the brain and the cavity of the 

 skull are quite dry. 



26. After the " bag experiment," salt solution (Method 1) can no 

 longer be absorbed, and can no longer be driven through to a hole in 

 the lumbar region, but acts in the same way and produces the same 

 effects as the bag. 



27. Marked physiological effects occur in the cat when the intra- 

 cranial pressure is raised 10 mm. Hg above the normal. The measure- 

 ment is taken over the medulla oblongata. 



28. The venous pressure in the cavity of the occipital protuberance 

 falls to zero when the " bag " is distended over the parietal region, 

 i.e., the entrance of blood is obstructed ; the exit by the bony trans- 

 verse sinuses remains open. (Method 4 .) 



29. The venous pressure in the superior longitudinal sinus rises 

 when the " bag " is distended, i.e., the exit is obstructed by the 

 cannula, and blood is forced out of the tributary veins into the sinus. 

 (Method 4 /3.) 



30. The normal venous pressure in each case at once returns when 

 the bag is emptied. 



Conclusion. November 18, 1893. 



The capacity of the intra-cranial cavity can be diminished by the 

 introduction of a foreign body into the subdural space. The first 

 effect of the diminution is to expel the cerebro-spinal fluid. After its 

 disappearance, further diminution of the space can only take place 

 by equal diminution of the volume of the intra-cranial blood vessels, 

 particularly of the veins and capillaries. The restriction or arrest of 

 the cerebral circulation thus produced is t)& efficient cause of the physio- 



