VENTILATION OF LINGS 351 



of oxygen for ordinary purposes. As a matter of faet a difference 

 in pressure of less than 4 nmi. would ])e quite sufficient to ensure 

 the supply of the 330 c.c. per minute required by the average man 

 resting but awake. 



How is the rate of transference increased to meet the needs of 

 the man doing hard muscular work who uses up 3,000 c.c. of oxygen 

 per minute ? One very obvious point of difference between a 

 resting and a working man lies in the volume of air passing into 

 the lungs per unit of time. The following table (LII.) shows that the 

 ventilation of the lungs is markedly increased by the performance 

 of work. 



TABLE LII 

 Ventilation of Lungs 



Litres per iiiiu. Kosijir. ]kt niiii. 



Resting 6-7 13-14 



Walking 24 14 



Running ..... 60 15 



Swimming in cold water . . . 90 — 

 Running up and down stairs (greatest 



possible effort of a noted "Swimmer) . 190 over 60 



That is, by the constant addition of fresh air to the lungs the 

 tension of oxygen in the alveoli is kept from falling. A tenfold 

 increase in ventilation provides an ample margin for even the 

 most strenuous work. 



Those who hold to the secretory hypothesis maintain that 

 while diffusion is capable of providing a sufficient oxygen supply 

 for a normal existence even with hard muscular work, yet when 

 the pressure of oxygen in the lung is brought much below normal, 

 active secretion by the lung epithelium must be brought into 

 play. Aviators, for instance, rise to great heights, and so come 

 under a low barometric pressure. 



Height above sea level 

 in metres. 





 1,000 

 2,000 

 3,000 

 4,000 

 5,000 

 6,000 

 7,000 



It is well known that ballooning, for instance, causes respiratory 

 distress ; so, too, does mountaineering. Mountain sickness fre- 



