274 Increase of Intracranial Pressure or Tension. [June 19, 



the same time the measurement of the amount to which the cranial 

 content had been lessened. 



The results are divided into two classes : 



T. Those in which the pressure was made on any part of the 



brain. 



II. Those in which it was made by passing the bag into the cavity 

 of the 4th ventricle. 



In the former case the heart, the blood pressure, and the respira- 

 tion were all affected in varying degrees ; in the latter case it was 

 found possible to separate the effect upon the heart, the blood pressure, 

 and the respiration respectively. 



The following is a summary of the chief results obtained : 



I. The Heart. A considerable increase of the intracranial tension 

 was required to influence the heart; it became slowed and finally 

 arrested. This happened more readily after respiration had ceased, 

 and required a higher pressure to produce it when artificial respira- 

 tion was employed, whilst division of both vagi nerves abolished any 

 slowing or arrest. The arrest, when produced, continued permanently, 

 unless the pressure was quickly removed, or artificial respiration 

 employed, or the vagi divided. But if the pressure was maintained 

 whilst artificial respiration enabled the heart to start again, 

 then the cardio-inhibitory influence was gradually lost, so that the 

 heart returned from being very slow to its normal rate, or increased 

 beyond the latter until the rate became equal to that seen after 

 division of the vagi. When the vagi were divided at this stage the 

 rate of the heart did not alter. But if the pressure were removed, 

 and a pause made (the vagi being intact), the cardio-inhibitory 

 control was gradually regained, so that the heart could be slowed, or 

 arrested afresh. 



The Blood Pressure. A primary rise, small in the dog, larger in 

 the monkey, was followed by a fall distinct from that produced by the 

 slowing of the heart, and not necessarily accompanying it. When the 

 heart started again the blood pressure rose, finally reaching the level 

 seen after division of the vagi, so that no further rise took place when 

 this was done. But the power of producing a fall of blood pressure 

 was easily lost, for when the intracranial tension was raised for the 

 second time no fall took place, and the blood pressure continued at a 

 normal level or above, even although the heart was greatly slowed. 

 After division of the vagi the blood pressure was raised by increasing 

 the intracranial tension and by artificial respiration, so that it could 

 be maintained at a level between 300 and 400 mm. Hg for consider- 

 able periods. 



Respiration. This was likewise impaired and arrested. Its arrest 

 reacted upon the heart and the blood pressure upon it, so that after 



