1906.] 



The Pharmacology of Ethyl Chloride. 



407 



passes off, the heart's rate increases and the blood-pressure rises to its former 

 level. Another set of respirations is then taken and the same cycle of events 

 follows. In this manner respiratory arrest is delayed. The animal is, 

 however, becoming asphyxiated, so that either the heart must be arrested by 

 the consequent exalted irritability of the vagi or the respiration cease. One 

 of these occurrences is found by experiment to occur. This form of respira- 

 tion does not always precede respiratory failure. It occurs generally when 

 excessively large percentages of ethyl chloride are administered in the air. 



Fig. 11. — | size of original. 



In some experiments respiration failed independently of a fall in blood- 

 pressure. In this case the respiration may remain in abeyance for 

 considerable periods (6' to 7') without the blood-pressure being depressed, and 

 subsequently continue in a normal manner. 



The comparison of these results with those of chloroform (12) indicates 

 that 10 per cent, of ethyl chloride vapour produces approximately the same 

 effects upon the respiration as 2 - 5 per cent, of chloroform vapour in the 

 air inspired. This quantitative relation is about the same as that which 

 was found to obtain in the case of stimulation of the vagus mechanism by 

 these two agents (p. 401). 



In none of these experiments was it found that the heart was arrested 

 before the respiration. Since, however, slowing of the heart usually began 

 before the respiration showed signs of stoppage, it is possible that the heart 

 vol. lxxviii. — b. 2 I 



