46 RESPIRATORY EXCHANGE OF ANIMALS AND MAN 



A very ingenious respiration apparatus has been constructed and 

 used by Hanriot and Richet [1891]. They use three equal gas meters. 

 One measures the inspired air, a second the expired air, and a third the 

 expired air after absorption of the carbon dioxide in a suitable absorber. 1 

 The difference in reading between the second and third meter shows 

 the amount of carbon dioxide eliminated during a certain time, while 

 the difference between the first and third shows the oxygen absorbed. 

 The experiments made by Hanriot and Richet are not particularly 

 accurate, but in the writer's opinion there is no doubt that the 

 possibilities of this method are great. With modern gas meters of 

 sufficient size placed in one water-bath volumes can be measured ac- 

 curately to To,WiJ> anc * arran g emen ts could easily be made giving a con- 

 tinuous graphic record of ventilation, oxygen absorption and carbon 

 dioxide output. 



The use of gas meters for measuring non-continuous air currents 

 requires certain precautions to which due regard has not always been 

 paid. The volume recorded by a meter is independent of the rate 

 only within a certain limit, corresponding roughly to 100 complete 

 revolutions per hour. At higher rates the volumes recorded are 

 smaller than what has actually passed (Benedict [1912]), but with a 

 constant high rate it can still be determined without appreciable error 

 provided the meter is calibrated at the rate desired. With a non- 

 continuous current, as in measuring expirations, the rate varies from o 

 to a maximum at the height of expiration. This maximum corre- 

 sponds roughly to about three times the total ventilation, and when a 

 meter shall measure the expiration accurately the maximum rate 

 should not be above 100 revolutions per hour. The ventilation of a 

 man at rest is something like 400 litres per hour, and the meter em- 

 ployed for measuring the ventilation should not therefore measure less 

 than 12 litres per revolution. During muscular work the ventilation 

 may easily rise to 4000 litres, requiring for its measurement a meter 

 with a drum of 1 20 litres capacity. 



In respiration experiments on animals it is frequently desirable or 

 necessary to suppress all voluntary movement by means of curari. 

 Recourse must then be had to artificial respiration. A number of de- 

 vices have been described for performing artificial respiration and 

 several of these can be combined with respiration apparatus. A 

 very simple and effective form, which has been used successfully in 



1 H. and R. used potash solution flowing down over glass beads, but soda lime would 

 undoubtedly absorb much better and be easier to use. 



