10 
DR. W. MARCET OX A CIIEillCAL IXQUTRY IXTO 
pipe about an inch in diameter, opening under the dome of the bell-jar. But this still 
proved insuliicient, as it was necessary to devise some method enabling the person 
under experiment to breathe without his being aware that his breath was being 
collected for experiment. The difficulty was overcome as follows :—A double-way 
stop-cock, with passages not much less than an inch in diameter, was fixed to an 
upright stand screwed to the floor, and an india-rubber tubing of a corresponding 
diameter was connected with it, long enough to be used by a person sitting in a 
recumbent posture in a deck chair-—there was a vulcanite mouthpiece in the distal 
end of the india-rubber tube. By means of a handle the double-way cock could be 
turned in such a position as to enable the person sitting in the deck chair to breathe 
either into the open air or into the bell-jar. A little silk flag placed inside a glass tube 
introduced in the course of the india-rubber tubing, flapped during the expiration and 
remained still while air was inspired, thus acting as a guide throughout the experi¬ 
ment. This ai'rangement answered the purpose in every way ; the person experi¬ 
mented upon was instructed to inspire through the nose and expire through the tube 
while in communication.with the open air, and without paying any attention to the 
bell-jar, the little flag showing clearly the time when the respiration had become 
perfectly slow and natural. Then, without giving any notice and unknown to the 
person under experiment the handle of the double way cock was turned during an 
inspiration and the expired air directed towards the bell-jar ; this was so delicately 
suspended that no appreciable difference of sensation was experienced in the 
breathing, and it frequently happened that the bell-jar was half way up while the 
person in the chair still thought he was breathing into the outside air. In order to 
deviate in no way from natural respiration in these experiments, no valvular face- 
piece was used, the air, as stated above, being inspired through the nose and expired 
through the mouth. A little practice made it quite easy, but in order to ensure 
absolute accuracy the two persons who submitted to experiment closed their nose 
during expiration by a light pressure with the index finger of each hand held in 
such a position as to do this with as little effort as possible. After a time the 
movement became quite automatic, and it was too slight to cause the addition of any 
appreciable amount of carbonic acid in the expired air. 
The experiment was made in the following way :—The person sat in a semi- 
recumbent posture in a comfortable deck chair, his body and legs being thoroughly 
supported and the feet resting on a stool at the same height as the legs, thus every 
muscular strain was done away Avith. Then he began inspiring through the nose and 
expiring from the mouth through the india-rubber tube and double-AAmy cock into the 
open air ; at first the little flag in the track of the an expired was seen to fly about 
wildly, then by degrees its movements became more regular, and after from ten 
minutes to a quarter of an hour the respirations were observed to be quite quiet and 
steady. The scale of the bell-jar being at 0° the stop cock was turned during an 
inspiration, and the air ex[)ired directed into the bell-jar. Tlie instant the bell-jar 
