RESPIRA TION. 4 1 7 



loose chemical union in both the plasms and the corpuscles. That which is in 

 chemical combination in the plasma is probably in part combined with glob- 

 ulin and alkali, and in part with sodium as carbonate and bicarbonate, the 

 proportion of each varying with the tension of the C0 2 . The white blood- 

 corpuscles, so far as they contain any of the C0 2 , hold it probably in com- 

 bination with globulin and an alkali, and as carbonates of sodium. The great 

 bulk of the gas disengaged from the corpuscles is derived from the red cells, 

 but in what combination or combinations it exists is not positively known. 

 The experiments of Setschenow, Zuntz, Bohr, 1 and others indicate that it is 

 associated in some obscure way with haemoglobin which seems to have the 

 pow T er of combining with C0 2 . This latter fact has been shown by the experi- 

 ments of Bohr, who compared the quantities of C0 2 absorbed by pure water and 

 by solutions of pure crystallized haemoglobin at constant temperature and varied 

 pressure. He found that the weight of CO, absorbed by the water increased reg- 

 ularlv with the increase of pressure, whereas the quantity absorbed by the solu- 

 tion of haemoglobin was very large relatively to the lower pressures and small 

 for higher pressures, and that the increments of absorption were in decreasing 

 ratio to the rise of pressure. The absorption curve is therefore steep at first, 

 becoming less and less so with the increase of pressure, and entirely different 

 from the absorption line for pure water, which is straight. Moreover, the 

 quantity of C0 2 dissolved was considerably in excess of that which physical 

 laws could permit. It is not improbable that the O combines with the pig- 

 ment portion of the haemoglobin, and the C0 2 with the proteid portion. The 

 CO.,, in whatever form or forms it may exist in the red corpuscles, is in looser 

 combination than in serum. 



Strassburg's experiments show that the average tension of C0 2 in arterial 

 blood is 21.28 millimeters of Hg, or 2.8 per cent, of an atmosphere, and in 

 venous blood 41.04 millimeters, or 5.4 per cent, of an atmosphere. 



Tension of N. — The quantity of nitrogen in the blood is about 1.8 volumes 

 per cent. It is in simple solution in the blood-plasma, and the quantity in 

 both venous and arterial blood is practically the same, its presence and quan- 

 tity are not of physiological importance. Argon has been found in the blood 

 of the horse by Regnard and Th. Schlosing Sohn. 2 



The Interchange of O and C0 2 between the Alveoli and the Blood. — 

 Let us now inquire into the factors which bring about the passage of O from 

 the alveoli to the blood and of CG 2 from the blood to the alveoli. If we have 

 two mixtures of the same gases, but in unlike proportions, and separate them 

 by means of an animal membrane, diffusion will occur through the membrane 

 until the partial pressures of the two gases are the same on the two sides of the 

 membrane. Now modify this experiment by bringing an atmosphere of air 

 in contact with water containing O, C0 2 , and N in solution or in chemical 

 combination: if the partial pressure of O in the air be greater than the tension 



1 /-.'xprr. I'ltirrsnch. u. d. Sauerstoffnaufnahme d. Blutfarbstoffes, Copenhagen, 1885 ; Beilrage zur 

 Physiology, Festechr. f. ('. Ludwig, 1887, pp. 1H4-174. 



2 Comptes rendus de I' Acad, des Sci., 1897, t. 124, p. 302. 



Vol. I.— 27 



