1894.1 On Infra Cranial Pressure. 53 



mechanic's tap, and a brass tube of about 2 inches in length screwed 

 into the hole. This tube is connected with a burette containing salt 

 solution at the temperature of the animal. A clip is interposed 

 between the burette and the brass tube, and the burette connected 

 with a pressure apparatus. 



By this method salt solution can be driven into the subdural space 

 in measured amounts and at varying rates. 



ft. If, before introducing the brass tube, a bag of very thin india- 

 rubber is tied on to the end of it (the arrangement being otherwise 

 the same), measured amounts of salt solution can be repeatedly 

 introduced or withdrawn from the bag within the subdural space. 



2. Measurement of the Normal Intra-cranial Pressure or Cerebral 

 Tension. 



<x. A trephine hole is made, " wormed," and filled with warm salt 

 solution. A piece of brass tube is screwed in, over the end of which a 

 membrane of very thin india-rubber has been tied. The brass tube 

 is connected with the intervention of a piece* of fine-bored glass 

 tubing with a ~J~-piece, one branch of which leads to a pressure bottle, 

 the other to a mercurial manometer. The apparatus is completely 

 filled with water, excepting that a bubble of air is introduced within 

 the glass tube so as to act as an index. 



The normal position of the air index is marked on the glass tube 

 before the apparatus is screwed into the trephine hole. On screwing 

 the apparatus in, the air index, which is at first forced out, is brought 

 back again to the normal position by raising the pressure bottle. 

 The manometer records the normal intra-cranial pressure. 



/3. A trephine hole is made and " wormed," and the dura mater is 

 then freely divided. 



The measuring apparatus is filled with 0*6 per cent, salt solution, 

 instead of water, and an air index is introduced within the glass 

 tubing. No membrane is placed upon the end of the brass tube, so 

 that when the tube is screwed in its cavity freely communicates with 

 the subdural space. The pressure bottle is now raised till the air 

 index begins to move inwards. The manometer records the pressure 

 which is necessary to balance the normal intra-cranial pressure. Any 

 excess drives salt solution into the subdural space. 



3. Measurement of the Variations of Intro-cranial Pressure produced 

 by the above Methods (1 a. and ft). 



With the measuring apparatus (2 *) the variations can be accu- 

 rately measured and recorded graphically. For when by increase of 

 intra-cranial pressure the air index is displaced outwards it can be 

 brought back again to its initial position by raising the pressure 

 bottle to the required amount, and when by decrease of intra-cranial 

 pressure the air index is sucked inwards it can, in like manner, be 

 brought back again to the mark by lowering the pressure bottle. In 



