INNERVATION OF THE RESPIRATORY MOVEMENTS. 693 



was reduced. This change did not affect the quantity of carbon 

 dioxid in the blood. The following results were obtained: 



Normal air volume breathed per minute = 7,325 to 9,000 c.c. 



Air with 10 to 11.5 per 



cent, oxygen " " " " = 8,166 to 9,428 " 



Air with 8 to 10 per cent. 



oxygen " " " " = 9,093 to 12,810 " 



A reduction of one-half of the oxygen in the air breathed had little 

 effect upon the respirations. A similar conclusion may be drawn 

 from Haldane's experiments* with carbon monoxid. He found 

 upon breathing mixtures of this gas that no distinct effects were 

 observable until the blood was about one-third saturated with 

 the gas, — that is, had lost one-third of its oxygen. Haldane 

 states that when the oxygen in the air breathed is reduced 

 from 20.9 per cent, to 14 or 15 per cent., a concentration of 

 oxygen in which an ordinary flame will be extinguished, there is no 

 perceptible disturbance in breathing. If, however, a further re- 

 duction is made suddenly to 7 or 8 per cent, there is marked panting 

 and the lack of oxygen in the blood is indicated by the blue color of 

 the face. If the diminution in oxj^gen is effected gradually, as 

 happens, for example, when a person rebreathes the au- in a 

 confined space (provision being made for the absorption of the 

 COo), the effect on breathing begins to appear only after the oxygen 

 pressure falls to about 13 to 14 per cent. At lower pressures of 

 oxygen the respiratory movements become increased in amphtude 

 and rate, but in a resting person the dyspnea does not become 

 excessive, as is shown bj^ the fact that an individual performing 

 this experiment of rebreathing will, unless watched, continue until 

 he falls unconscious from lack of oxygen. A similar experience is 

 recorded by balloonists for very high ascensions, 25,000 to 30,000 

 feet (see p. 705). Zuntz's experiments, in which the CO2 in the 

 air breathed was increased, while the oxygen remained normal, 

 gave quite different results, as follows: 



Normal air volmne breathed per minute, 7,433 c.c. 



Air of 20.2 per cent. O, 0.95 per cent. 



CO2.... " " " " 9,060 " 



Air of 18.06 per cent. O, 2.97 per cent. 



CO2 " " " " n,326 ". 



Air of 18.42 per cent. O, 11.5 per cent. 



CO2 " " " " 32,464 " 



These and similar result sf show that small differences in the 

 amount of the carbon dioxid in the blood have a very marked effect 



* Haldane, "Journal of Physiology," IS, 442, 1895. 



t See Haldane and Priestly, "Journal of Physiology," 32, 225, 1905., 



