The unloading of oxygen from the blood 171 



point of fact the venous Go-pressure was very small, the venous blood 

 was almost reduced, in the case when the animal was given only 4/ 2 

 to breathe ; and assuming the tissue O 3 -pressure p' in this case to have 

 had its minimum value of zero, it was even so not so very far from the 

 venous Go-pressure. Thus when p is greater, and p p less, p' must 

 be even closer to the venous O 2 -pressure than it was when p was 

 small. We see therefore that in the kidney the Go-pressure in the 

 tissue is determined very largely by the Go-pressure of the venous 

 blood, and is only definitely less than it when the venous pressure is 

 small owing to incomplete saturation of the arterial blood. 



It therefore seems that the kidney like the submaxillary is an 

 organ in which the oxygen pressure in the tissue approaches that in 

 the venous blood, which, in the renal veins of animals breathing 

 normally, is remarkably high. Further than this we cannot make any 

 statement about the quantitative values of oxygen pressure in the 

 tissues except that in such organs as the parotid and the sublingual 

 the conditions are likely to be similar to those prevailing in the sub- 

 maxillary. 



We have then two distinct types : in the first class the difference 

 between the final capillary pressure and the tissue pressure is so 

 small that the tissue oxygen pressure approximates to the pressure 

 of oxygen in the venous blood; in this class are the glands which 

 have been studied. In the other class, that of skeletal muscle, the 

 difference between the capillary pressure and tissue pressure is so 

 large that the latter is 25 mm. or less in the cases measured. In the 

 former organs the blood flow can be considerably diminished without 

 diminution of the oxygen taken in by the organ, in the latter it 

 cannot. 



REFERENCES 



(1) Verzar, Journal of Physiol. XLV, p. 39, 1912. 



(2) Barcroft and Miiller, Ibid. XLIV, p. 259, 1912. 



