THE PHEHOMEHA OE HUMAH HESPIRATiOH. 
9 
The following investigation was earned out in a laboratory of the Physiological 
Department at University College, which Professor Schafer has kindly placed at my 
disposal. Two persons—my assistant, Mr. 0. F. Townsend, and my laboratory 
attendant, William Alderwood, who has worked for the last five years in my 
laboratory, and whom I can thoroughly trust to carry out my instructions—both 
kindly submitted to experiment. 
The incpiiry has to be prefaced with a statement of the method of investi¬ 
gation adopted. The main objects w^ere to collect and measure the air expired from 
the lungs within a given time, and then find out, as accurately as possible, the weight 
or volume of carbonic acid it contained. I had proposed at first to determine also the 
volume of air inspired, but met with so many difficulties in carrying this out satisfac¬ 
torily that it was given up. There are two possible sources of error in a work of this 
kind, first on account of the resistance breathing has to overcome when the expired 
air is either collected for analysis or passed through absorbing media; and, secondly, 
from the attention of the person who is breathing being directed to the expeii- 
ment, so that respiration becomes a voluntary act instead of being purely automatic. 
In Edward Smith’s experiments*' the air was inspired through a dry gas meter, and 
expired through a succession of vessels which absorbed the water and carbonic acid, 
the latter being estimated by weighing. This method, although possessed of the 
advantage of allowing each experiment to be continued for an indefinite length of 
time, appeared to me hardly delicate enough for the object I had in view, especially 
because of the unavoidable resistance to free respiration, although it might be but 
slight. The air expired had therefore to be collected in a bell-jar, in such a way 
that the person under experiment might not be aware, at the time, that he was 
breathing with an object in view. I had two bell-jars constructed for this purpose 
by Messrs, W. Parkinson and Co., engineers, by whom they were admirably made. 
Each bell-jar could hold 40 litres of air, and was graduated on a scale into litres and 
fractions of litres. They were made of japanned iron, and suspended over taidxs filled 
with a solution of pure sodium chloride ; the solution in the tank used for most of 
the experiments had a density of 1'074, corresponding to 10 per cent, of sodium 
chloride. The tanks had an annular form, so that the fluid should expose as small a 
surface as possible to the air contained in the jars. The bell-jars were counterpoised 
over a pulley fixed to a cycloid to winch another regidating weight was suspended. 
The cycloid was so constructed that the increased leverage of the regulating w^eight 
counterbalanced exactlv the increase of weiodit of the bell-iar as it ascended from the 
J O J 
tank and vice versd. A gauge fixed to the dome of the bell-jar and charged with 
almond oil indicated the state of tension of the air in the jar. I found that by keeping 
the outside of the bell-jars carefully lubricated with almond oil their motion through 
the salt water was certainly facilitared, and after careful adjustment the bell-jars were 
so nicely suspended that air could be expired quite unconsciously into them through a 
* ‘ Phil. Trans 1859. 
C 
MDCCCXC.— B. 
