170 Chapter X 



It is clear then that in this experiment there was a positive 

 pressure oxygen in the tissues during Period I. I picture the course 

 of the experiment thus : as the value of C fell along the line C l (7 2 , 

 that of T fell along a parallel line T l T x until it reached zero, after 

 which the intra-cellular pressure would remain at zero and the 

 quantity of oxygen diffusing out of the vessels would vary with the 

 intra-capillary pressure. The other two experiments quoted by 

 Verzar are intermediate between these two. 



It seems to me to be certain (1) that there is a greater difference 

 between the venous oxygen pressure and the intra-cellular oxygen 

 pressure in muscle than in the submaxillary, (2) that the blood 

 therefore does not leave the muscle in equilibrium with the tissue, 

 (3) that there is at times a definite though small pressure of oxygen 

 in resting muscles. 



Two other organs have been investigated, namely the kidney and 

 the heart. Of the latter we have nothing certain to say. It proved 

 impossible with varying capillary pressure to keep the quantity of 

 oxygen used by the heart constant. In that respect it resembled 

 muscle. On the other hand it also proved impossible to maintain 

 the beats at a constant rate under conditions of oxygen want. With 

 regard to the kidney very interesting results were obtained, but they 

 were also less simple than in the case of muscle and the submaxillary 

 gland. When the capillary pressure of oxygen falls, the amount used 

 by the kidney (Q) rises provided that the amount of oxygen brought 

 to the kidney is at least sufficient to allow it to rise. 



For the moment I will pass over the interest of this as a problem 

 in metabolism and consider it solely as a problem in physics. It is 

 clear that whatever be the need of the cell for oxygen there cannot 

 be less than no oxygen pressure in it. Therefore let us consider the 

 limiting case where p = 0. 



At this point Q is observed experimentally to have, and therefore 

 (p >') must have, its maximum value. With higher values of the 

 capillary pressure p, Q is observed experimentally to be less, and 

 therefore (p p) must be less. Thus p', the tissue pressure, can no 

 longer be zero, but must be even nearer to p the average capillary 

 pressure than it was before. But p' can in any case not be greater 

 than the venous pressure of oxygen, for otherwise the blood could 

 never by diffusion have got reduced to its venous condition. But in 



