622 



PRINCIPLES OF GENERAL PHYSIOLOGY 



in 



surfaces (adsorption) is also accompanied by the evolution of heat, as would indeed be expected 

 from the compression, or perhaps liquefaction, involved. If we take, for example, the values 

 obtained by Titoff(1910), we find that the heat evolved in the adsorption of various gases by 

 charcoal is of the same order as the values of the "heat of combination" of haemoglobin with 

 oxygen. Thus: at 0, 1 g. of charcoal adsorbed 0"259 c.c. of nitrogen under a pressure of 

 10"2 mm. of mercury, with a development of heat of 0'373 calorie per c.c. adsorbed. The 

 corresponding values for carbon dioxide and ammonia are about 0'33 and 0'4 calorie. One 

 gram of haemoglobin at room temperature takes up 1'34 c.c. of oxygen, and gives off 1'85 

 calories, that is, 1'37 calories per c.c. If we take Torup's result, we have 0'41 calorie per c.c. 

 oxygen taken up. I merely call attention to the fact, without drawing conclusions. 



Effect of Salts and of Acid. The dissociation curve of pure haemoglobin, as we 

 have seen, can be expressed by the equation to a rectangular hyperbola. If, 

 however, we compare this curve with that given by Bohr for haemoglobin as 



present in blood, we see that 

 the latter has a different shape. 

 Now, it was shown by Barcrof t 

 and Roberts (see Bancroft's 

 book, 1914, p. 22) that Bohr's 

 curve is correct for normal 

 blood, and that if the blood is 

 dialysed, the first form, similar 

 to that obtained by Htifner 

 with pure solutions of haemo- 

 globin, is obtained. Fig. 191 

 is a reproduction of one given 

 by Barcroft and Roberts. 



The physiological import- 

 ance of this fact is similar to 

 that referred to above in con- 

 nection with temperature. In 

 the presence of salts, haemo- 

 globin gives off its oxygen 

 more readily, so that if the 

 oxygen tension in the tissues 

 has fallen to 10 mm. of 

 mercury, the percentage 

 saturation of the haemoglobin 

 of the blood may be reduced 

 to 25 per cent., whereas, if 

 the haemoglobin were in pure 



100 



BO 



80 



BO 



50 



40 



30 



10 



10 20 30 40 50 60 70 80 90 100 



FIG. 192. EFFECT OF CARBON DIOXIDE ON THE DIS- 

 SOCIATION CCRVE OF HEMOGLOBIN IN THE BLOOD. 



Ordinates percentage saturation. 



Abscissae oxygen tension. 



Uppermost curve with 3 mm. mercury carbon dioxide tension. 



Middle curve with 20 mm. 



Lowest curve with 90 mm. 



(Barcroft and Poulton, "Proc. Physiol. Soc.' 

 in Jl. Physiol. , 46, p. iv. ) 



solution in water, it would 

 only be reduced to 55 per cent, 

 of saturation. 



The effect of acid is the 



same as that of salts, but more marked (see Fig. 192). Investigation shows that 

 the effect is due to the hydrogen ions. Again, its importance is obvious. All 

 cells produce carbon dioxide in activity and muscle in particular produces lactic 

 acid. Both facilitate the giving off of oxygen to the active cells. 



Christiansen, Douglas, and Haldane (1913) show that the amount of carbon 

 dioxide taken up by blood is greater by one-tenth when the haemoglobin is reduced 

 than when saturated with oxygen. Venous blood can, therefore, take up more 

 carbon dioxide at the same tension than arterial blood can. As the blood takes 

 up oxygen again in the lungs, this carbon dioxide is more easily given off. From 

 the adsorption point of view, this fact is not difficult to explain. According to 

 Freundlich (1909, p. 116), and the experimental results of Hempel and Vater 

 '(1912), from a mixture of solutes each constituent is adsorbed and the relative 

 proportion is governed by their relative powers of lowering surface energy, but 

 even that one which lowers surface energy most is adsorbed less than from a 

 pure solution. Hence it appears that the lower the tension of oxygen, the more 

 carbon dioxide would be adsorbed, and the lower that of carbon dioxide, the 



