BY H. S. HALCRO WARDLAW. 813 



effective difference of tension between the gases of the alveolar 

 air and the gases of the venous blood may be altered. 



Summary. 



1. When the normal ventilation of the lungs is discontinued 

 bv holding the breath, the alveolar tensions of carbon dioxide 

 and oxygen may be expressed as exponential functions of the 

 period for which the breath is held. 



2. When the normal ventilation of the lungs is discontinued 

 by breathing into and out of an empty bag, the alveolar tensions 

 of carbon dioxide and oxygen may l)e expressed as exponential 

 functions of the period for which the contents of the lungs are 

 lebreathed. 



3. The rate of the gaseous exchange in the alveolar air is 

 about twice as great when the movements of breathing are per- 

 formed, as when the breath is held under normal pressure. 



4. The rate of gaseous exchange in the lungs is also increased 

 to the same extent when the breath is held under pressures less 

 than that of the atmosphere by a certain amount. 



5. Holding the breath under pressures greater than that of the 

 atmosphere slightly decreases the rate of respiratory exchange. 



6. The rate of the gaseous exchange, when the renewal of the 

 air in the lungs is prevented, is not afiected by the depth or 

 frequency of the respiratory movements during the period of 

 these experiments. 



In conclusion, I wish to express my thanks to Professor Sir 

 Thomas Anderson Stuart, in whose laboratory this work was 

 done, to Dr. H. G. Chapman, whose advice and criticism were 

 of the greatest value, and to Miss K. C. Pinkerton, B.Sc, who 

 assisted in the preliminary experiments. 



REFERENCES. 



Becher, Die Kohlensaurespannung ini Blute. Zurich, 1855. From 

 Henle and Meissner's Ber. iiber d. Fortschr. d. Anat. u. Physiol, 

 im Jahre 1856, 249, 1857. 



du Bois-Revmond, Arch. f. Anat. u. Physiol., physiol. Abt., 257, 1910. 



