1894.] On Intra- Cranial Pressure. 55 



6. Salt solution (0'6 per cent.) can be slowly driven into the sub- 

 dural space at the rate of about 1 c.c. a minute, without raising the 

 intra-cranial pressure or producing any physiological effects. As 

 much as 20 c.c. has thus been driven in during one experiment. 

 (Method 1 *.) 



7. Salt solution can be driven through from the parietal hole to a 

 hole in the lumbar region of the spinal column. The whole of the 

 subdural space can thus be syringed through. 



8. Salt solution cannot be driven from a hole in the lumbar region 

 out of a hole in the parietal region. The brain floats up and closes 

 the parietal hole as a valve. 



9. Salt solution, if driven in quickly with a higher pressure, pro- 

 duces a momentary rise of intra-cranial pressure and momentary 

 physiological effects. These disappear very rapidly as the solution is 

 absorbed. 



10. On introducing 0'5 c.c. of salt solution within a bag in the sub- 

 dnral space of a cat (Method 1 /3), no rise of intra-cranial pressure 

 occurs, and no physiological effects are produced. 



11. The introduction of more than 0'5 c.c. produces a lasting rise 

 of intra-cranial pressure and physiological effects. These are : 

 (1) slowing to stopping of respiration; (2) rise of blood pressure 

 and slowing of the heart ; (3) dilatation, or extreme constriction, of 

 the pupil, and sometimes nystagmus. 



12. The cat may become habituated to the smaller degrees of 

 heightened intra-cranial pressure, and the physiological effects pass 

 off. 



13. Greater amounts than 1 c.c. cause an enormous and maintained 

 rise of arterial pressure, with acceleration of the heart, inspiratory 

 gasps at long intervals, followed by fall of arterial pressure and 

 death. 



14. 0'5 c.c. is the largest amount of displacement which can be 

 perfectly compensated for in the cat, i.e., this is the reduction of the 

 cranial capacity which can be made up for by escape of cerebro- 

 spinal fluid. 



15. The brain of the cat of ordinary size, measured up to the level 

 of the calamus scriptorius, equals in volume 26 c.c. 



16. The amount of compensation is reduced to nothing on repeating 

 the experiment a second time, and the effects which follow the intro- 

 duction of the same quantity of salt solution into the bag are much 

 more marked. 



17. In the dog of the fox-terrier size the amount of compensation 

 is 1'5 c.c. 



18. The brain of the ordinary fox-terrier, on an average, equals 

 64 c.c. in volume. 



19. The introduction of more than 1'5 c.c. in the dog produces 



