iQoo-i.] Observations on Blood Pressure. 205 



anjemia of the brain produced by t3''ing both carotids and both 

 vertebral arteries produces little if any change as a rule in the 

 respiration. From this fact they were led to the conclusion that, " The 

 respiratory centres are remarkably insensitive to a lowering of their 

 blood supply." Further, I have frequently observed that the respiration 

 stopped while the pressure was still comparatively high, and only after 

 the cessation of the breathing did the pressure somewhat suddenly fall 

 to zero. Tracing 20 illustrates this point. One might say in fact that 

 the pressure only falls very low after the respiration fails and that 

 probably the stoppage of the respiration due to poisoning of the respira- 

 tory centre is the cause of this sudden extra fall in the already slowly 

 falling pressure. It seems that as the factors which maintain the blood 

 pressure become weakened by chloroform the respiratory pump 

 becomes more necessary to the upkeep of this pressure than it usually is, 

 and hence when it stops the pressure drops at once. Possibly, however, 

 an anaemic respiratory centre is more susceptible to the toxic effects of 

 chloroform than one not so anaemic, and this special susceptibility Mr. 

 Hill believes he has noticed along with others.^ 



When the blood pressure falls greatly from chloroform and 

 remains low, life must be endangered, but in my experience animals 

 do not die more easily from chloroform administered in the vertical 

 than in the horizontal position, and it is decidedly harder to kill 

 a dog with chloroform when the pressure is very low from 

 hemorrhage than when this is not the case. The second Hyderabad 

 Commission noted this point thus, " In Experiment III, the splanchnics 

 were divided, a proceeding which, as is often said, bleeds the animal 

 into its own vessels. The pressure was after this exceedingly low, 

 but chloroform was given and various other actions taken, and then 

 chloroform had to be pushed on a saturated sponge enclosed in a cap for 

 eleven minutes before the respiration ceased.'"' Again J. A. McWilliams 

 writes as follows,^ " The fall of blood pressure is in a certain sense 

 protective. It retards the continued access of the anaesthetic into the 

 vital organs. I have frequently been struck with the good resisting 

 power shown to the influence of both chloroform and ether in animals 

 in which a very low pressure was present due to other causes than 

 anaesthetics, e.g., vaso-motor paralysis." He rightly adds that, " On the 

 other hand the fall of blood pressure may become excessive and prove a 

 source of great danger." If then it is harder to kill a dog by chloroform 



1 "Causation of Chloroform Syncope," by L. Hill, British Medical Journal, April 17th, 1897. 



2 Second Hyderabad Commission Report. 



3 British Medical Journal, October, i8qo. 



