868 KESPIRATION AND OXIDATION. 



of the plasma is of importance in the giving up of oxygen to the tissues, 

 as the blood corpuscles contain a supply of oxygen only sufficient to 

 replace that removed from the plasma by the tissue. This quantity 

 of oxygen, which is dissolved in the plasma and at the disposal of the 

 tissues, is dependent upon the oxygen tension in the blood and only 

 indirectly dependent upon the total quantity of oxygen in the blood. 

 As this tissue is almost or entirely free from oxygen, a considerable dif- 

 ference in regard to the oxygen pressure must exist between the blood 

 and the tissues. The possibility that this difference in pressure is suf- 

 ficient to supply the tissues with the necessary quantity of oxygen is 

 hardly to be doubted. 



The animal body, it seems, also has the command over means of regu- 

 lating and varying the oxygen tension, and such a means is the carbon 

 dioxide produced in the tissue which, according to BOHR, HASSELBALCH, 

 and KROGH, 1 raises the oxygen tension. This is of special importance 

 when the tension of the oxygen in the blood of the capillaries is very low; 

 then the ability of the carbon dioxide to raise the dissociation tension 

 of the oxyhaemoglobin comes into play, especially with low oxygen tension. 

 Another regulating moment is, BOHR claims, the specific oxygen capacity 

 of the blood, which means the relation of the maximum oxygen combina- 

 tion to the quantity of iron of the blood or the haemoglobin solution. 



In regard to the carbon-dioxide tension in the tissue it must be 

 assumed a priori that it is higher than in the blood. This is found to 

 be true. STRASSBURG 2 found in the urine of dogs and in the bile a car- 

 bon-dioxide tension of 9 per cent and 7 per cent of an atmosphere, 

 respectively. The same experimenter has, further, injected atmospheric 

 air into a ligatured portion of the intestine of a living dog and analyzed 

 the air taken out after some time. He found a carbon-dioxide tension 

 of 7.7 per cent of an atmosphere. The carbon-dioxide tension in the 

 tissues is considerably greater than in the venous blood, and there is 

 no opposition to the view that the carbon dioxide simply diffuses from 

 the tissues into the blood according to the law of diffusion. 



Several methods have been suggested for the study of the quantitative 

 relation of the respiratory exchange of gas. The reader must be referred 

 to other text-books for details as to these methods, and we will here 

 mention only the chief features of the most important methods. It must 

 also be remarked, in regard to these methods, that those of REGNAULT 

 and REISET and of PETTENKOFER, determine the total gas exchange, 

 and indeed for a long time, while the other three methods determine the 

 respiratory gas exchange alone, and this only for a short time. 



1 Centralbl. f. Physiol., 17, and Skand. Arch. f. Physiol., 16. 



2 Pfliiger's Arch., 6. 



