BY H. S. HALrRO WARDLAW. 



80^ 



Table vi. 



Effect of uiereofted pressure on. a/reofar perceiifaye of carbon dioxide 

 after holding tht breath for JO neconds. 



These figures show, that holding the breath under increased 

 pressure certainly does not increase the gaseous exchange in the 

 lungs. Indeed, the average alveolar percentage of carbon 

 dioxide reached in 20 seconds, when the pressure in the lungs is 

 greater than atmospheric pressure, is lower than that reached 

 when the breath is held under normal conditions. 



The average deviation of the above results from the mean, 

 calculated as described by Krogh (1916), is iO'lo. This 

 numl)er is not much smaller than the amount bv which the 

 alveolar percentage of carbon dioxide, after holding the breath 

 under normal pressure, exceeds that found after holding the 

 breath for the same period under positive pressure. The results, 

 therefore, only show definitely that holding the breath under 

 increased pressure does not accelerate the gaseous exchange. 

 The differences observed are too small to allow any more precise 

 conclusions to be drawn from them. 



Negative pressures. — In Table vii., are given the alveolar per- 

 centages of carbon dioxide found after holding the breath for 

 definite periods, under pressures lower than that of the atmos- 

 phere. The control-determinations for normal pressure are 

 given also. In the last column of the Table, the figures are 



