1903.] 



Action of the Poison of the Hydrophidce, 



493 



the cessation of the heart's beat. The effect on the respiration was 

 simply a uniformly steady slowing down until convulsions set in, 

 when the breathing finally ceased at once. For example, in a rabbit 

 which had received a dose of 1 milligramme per kilo, directly into the 

 carotid artery (the artery being clamped immediately afterwards to 

 prevent haemorrhage), the respirations were 60 per minute imme- 

 diately before the injection of the poison. During the four minutes 

 immediately following the injection, the number of respirations were as 

 follows: — first minute, 56 ; second minute, 51; third minute, 42, and 

 the fourth minute 33. In the first quarter of the 5th minute they were 

 8, at which point convulsions set in and the breathing stopped. The 

 respirations were written down every quarter of a minute, and the 

 figures for the separate quarters show an equally steady diminution of 

 the number of respirations as the minute periods just given. In the 

 same experiment the pulse showed the following changes. Before the 

 injection it was 105 per minute. During the second half of the first 

 minute after the injection it was 47 (that of the first half minute was 

 lost), during the second minute it was 106, showing no alteration up 

 to this time. During the third minute it fell to 99, and during the 

 fourth it further fell to 48, that for its first half having been 32, 

 and for the second half 16. During this steady fall in the pulse rate, 

 its volume and force became increased. During the fourth minute, as 

 already mentioned, convulsions set in, and the pulse was lost for about 

 a minute, only the first and third quarters of the fifth minute having 

 been recorded as 8 and 11 beats respectively. During the last three 

 quarters of the sixth minute the beats were 15, 15 and 17 respectively, 

 being now very feeble instead of unusually full, as before the cessation 

 of respiration and onset of convulsions. During the first and second 

 quarters of the seventh minute, the beats were 26 and 20 respectively, 

 at which point the heart finally ceased to beat, that is, three and a half 

 minutes after the cessation of the breathing. Very similar results have 

 been obtained in another experiment, in which the same dose was injected 

 into the jugular vein, a steady fall in the respirations first occurring, 

 and they ceased with the onset of convulsions, while an equally steady 

 fall in the pulse rate occurred later than that of the respirations, 

 accompanied with an increased volume of the artery, the tension 

 rapidly falling when the respiratory convulsions set in, but the pulse 

 at the same time became more rapid again until it finally declined 

 once more and then ceased. These experiments appear to show that 

 the primary effect of the poison is a paralysing action on the respira- 

 tory centre, and that the cardiac failure is secondary to that of the 

 respirations. The exact explanation of the slowing of the pulse with 

 increased volume of the artery, I am not prepared to say without the 

 aid of pressure tracings, which I have not yet been able to take. 



VOL. LXXI. 



