818 CHEMISTRY OF RESPIRATION. 



From what has been said above (page 809) in regard to the internal 

 respiration, one can conclude that it consists chiefly that in the capil- 

 laries the oxygen passes from the blood into the tissues, while the car- 

 bon dioxide passes from the tissues into the blood. 



The assertion of ESTOR and SAINT PIERRE that the quantity of oxygen 

 in the blood of the arteries decreases with the remoteness from the^heart 

 has been shown to be incorrect by PFLiJGER, 1 and the oxygen tension in 

 blood on entering the capillaries must be higher. The oxygen tension 

 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 

 regulating and varying the oxygen tension, and such a means is the car- 

 bon dioxide produced in the tissue which, according to BOHR, HASSEL- 

 BACH, and KROGH, 2 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 dissocia- 

 tion tension of the oxy haemoglobin 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 combination to the quantity of iron of the blood 

 or the haemoglobin solution. 



As the haemoglobin prepared from different blood portions does not, according 

 to BOHR, always take up the same quantity of oxygen for each gram, so the 

 haemoglobin within the blood-corpuscle may show a similar behavior. He calls 

 the quantity of oxygen (measured at C. and 760 mm. Hg) which is taken up 

 by 1 grain of haemoglobin of the blood at 15 C. and an oxygen pressure of 150 mm. 

 the specific oxygen capacity? This quantity, he claims, may vary not only in 

 different individuals, but also in the different vascular systems of the same 

 animal, and it may also be changed experimentally by bleeding, breathing air 

 deficient in oxygen, or poisoning. It is now evident that one and the same quan- 

 tity of oxygen in the blood, other things being equal, must have a different ten- 

 sion according as the specific oxygen capacity is greater or smaller. The tension 

 of the oxygen, BOHR says, may be changed without changing the quantity of 

 oxygen, and the animal body must have means of varying the tension of the oxygen 



1 Estor and Saint Pierre with Pfliiger in Pfliiger's Arch., 1. 

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

 Centralbl. f. Physiol., 4, and Nagel's Handb. d. Physiol. 



