1906.] 



The Pharmacology of Ethyl Chloride. 



405 



saturated with air containing 30 per cent, of ethyl chloride vapour was 

 delivered to the brain as an independent arterial circulation, as described 

 above (p. 397). Inhibition occurring in these experiments, in which no 

 ethyl chloride comes into contact with the respiratory tract or the alveoli, 

 must necessarily be central. The inhibitory action of ethyl chloride is thus 

 similar to that of chloroform, and due to the direct action of the drug 

 upon the vagus mechanism in the medulla. 



Conclusions Eegaeding the Effect of Ethyl Chloride upon the Vagus 



Mechanism. 



(1) Yagus inhibition of the heart occurs very readily when ethyl chloride 

 vapour of a strength of 10 per cent, and upwards is administered in the air 

 inspired. 



(2) Sudden fall of blood-pressure occurring during the administration 

 of ethyl chloride vapour in the air inspired ranging in strength from 

 10 per cent, to 20 per cent, is due to vagus inhibition of the heart. During 

 the administration of 30 per cent, or upwards the fall of pressure is also 

 due to weakening of the cardiac and arterial musculature. 



(3) Cardiac inhibition is not so serious from ethyl chloride as it is from 

 chloroform, since it comes on before the spontaneous excitability of the heart 

 has been much depressed. It does not seem possible to permanently arrest 

 a dog's sound heart under ethyl chloride narcosis by vagus inhibition. It 

 requires 19 times more ethyl chloride to produce a given degree of cardiac 

 depression than is required of chloroform, whilst it requires only four times 

 as much to produce cardiac arrest by vagal stimulation, hence inhibition sets 

 in relatively rapidly. Herein lies the relative safety of ethyl chloride. 



(4) The cardiac inhibition arises from central stimulation. It is not reflex. 



(5) No evidence of any paralysis of vagus endings, such as was described 

 by Cole, was obtained. 



Inter-dependence of Blood-pressure and Eespiration. 



The investigation of this subject in chloroform narcosis demonstrated (12) 

 that the integrity of the nervous mechanism of respiration was dependent 

 upon the maintenance of blood-pressure. When the blood-pressure fell below 

 a certain level the respiration failed and recovered when the blood-pressure 

 rose again. In the present investigation of this subject in ethyl chloride 

 narcosis, simultaneous tracings were taken of the blood-pressure and 

 respiration with varying percentages of ethyl chloride vapour in the air 

 inspired and the results compared with those of chloroform mentioned above. 



