82 
author fixed on one young man on whom the effect was most 
regular for further experiment. It must be remembered, how- 
ever, that on no person was the effect small or uncertain. 
The objects of the farther experiments were these, 1st, to 
inquire if the influence could he observed when the amount 
of carbonic acid was small ; and 2nd, to separate the effects 
of the carbonic acid entirely from those of organic matter. 
With 3 per cent of carbonic acid evolved in the chamber 
itself, the pulse fell in 27 minutes from 67 to 62, the breath- 
ing rose from 17 to 23 ; the pulse so low that it was barely 
perceptible. The exposure was not full 27 minutes, as the 
gas took some time to evolve. 
With 2 per cent the pulse fell in 70 minutes 4, the 
breathing rose from 18 to 23^-. On coming out the pulse 
rose 8 in five minutes. 
With 1 per cent the pulse fell 4 in the hour. 
The following results were obtained by breathing air with 
carbonic acid entirely free from organic matter, the inspirations 
being taken from a prepared reservoir, and the expirations 
not being allowed to mix with them: — 
With 1 per cent C0 2 a rise of 2, then a fall of 5 beats of the 
pulse in 26 minutes. 
„ 0'5 pulse fell 5 in 40 minutes, respiration 
rose 7. 
„ 0*25 carbonic acid pulse rose 3, and fell 4 in 
30 minutes, respiration rose 4. 
„ 0*1 carbonic acid rose 1 and fell 1, in 45 
minutes, breathing rose 1. 
Ordinary air was breathed in the same way, so as to 
eliminate the effect of the apparatus. Pulse rose 1 and 
fell 1, but no greater change occurred during a whole hour. 
Breathing continued unchanged except at one interval, when 
it fell 1 and then resumed its usual number. In no experi- 
ment during the whole period did the breathing of the same 
experimenter ever fall 1 when there was as much as one tenth 
per cent of carbonic acid present. 
