88 THE NEW PHYSIOLOGY. 



below, what is usual for a man lying in bed and without 

 food. He is only short of oxygen in the sense that the 

 partial pressure of oxygen in the blood of his systemic 

 capillaries is too low for the proper support of lif e, though 

 there is still much oxygen left in even the venous blood. 

 When he was still moving about, just before being put 

 to .bed or laid on a stretcher, his oxygen intake was far 

 above that of a resting man. Yet probably his lips 

 were already blue, and he was in imminent danger of 

 sudden death from shortage of oxygen. This shows 

 clearly that not only must the blood supply an amount 

 of oxygen proportionate to the very fluctuating demands 

 at different times, but the oxygen must at the same 

 tune be distributed at a certain partial pressure or 

 concentration. When we measure the oxygen pressure 

 of the venous blood in a normal person it is extra- 

 ordinarily steady, in spite of considerable variations 

 in its rate of consumption. This relatively steady 

 normal is no longer maintained in the patient, and his 

 symptoms of oxygen-want are due, not to an abnormally 

 low rate of intake of oxygen, but to a failure in regulation 

 of the manner in which the oxygen is distributed. The 

 truth is that in a normal person the oxygen supply to 

 the tissues is, like everything else in the living body, 

 regulated minutely from minute to minute. To the 

 vis medicatrix of the sick body there thus corresponds 

 a vis directrix in the healthy body ; and just as the 

 vis medicatrix restores both structure and function in 

 the sick body, so the vis directrix regulates at every 

 moment the activities of the healthy body. The vis 

 medicatrix and vu- directrix are evidently one thing. 

 This is an old-fashioned and very gross method of 



