RESPIRATION 619 



no mention has yet been made, namely, the taking up of gases by surfaces such as 

 that of charcoal, adsorption, in which we certainly get a relation between the 

 amount taken up and the pressure. This was, in fact, suggested by Wolfgang 

 Ostwald (1908) as applying to the haemoglobin-oxygen system. But it is obvious 

 that it is very difficult to reconcile the fact that one molecule of haemo- 

 globin, when saturated, combines with one molecule of oxygen and no more, 

 with anything but a chemical compound as the final result. The key to the 

 puzzle will probably be found in a combination of the two processes. The amount 

 of oxyhaemoglobin would be determined by the amount of oxygen adsorbed on the 

 surface of the haemoglobin under a given pressure. At the same time, there are 

 difficulties in the treatment of the problem from this point of view, but it has, as yet, 

 received little attention. It seems clear that it is not permissible to use either the 

 law of mass action or the phase rule as applying to the case, until it has been 

 proved that they do or do not hold in the case of colloidal solutions, where there 

 must be surface phenomena intervening, although these phenomena may not be 

 as simple as when larger and flatter surfaces aie concerned. 



Taking pure haemoglobin in solution, and regarding the oxygen dissolved under 

 various pressures as its concentration, which is, by Henry's law, a function of the 

 pressures, Barcroft finds (1914, pp. 17-23) that the relative amounts of haemo- 

 globin and of oxyhaemoglobin which are present under a given oxygen pressure are 

 in accordance with the law of mass action. The curve is a rectangular hyperbola. 

 Under the hypothesis of adsorption, we should expect a parabolic curve. Under 

 certain conditions, as we shall see presently, results are obtained which correspond 

 more closely with such a curve. The greatest difficulty in the simple adsorption 

 hypothesis is, however, that already mentioned, namely, the ratio of oxygen to iron 

 or haemoglobin in complete saturation. 



However this may be, in respect to the function of haemoglobin in the organism, 

 the precise way in which oxygen is attached to it is of less importance than the 

 investigation of the ease and rapidity with which oxygen is taken up from the air 

 and passed on to the cells. It is especially here that the work of Barcroft and 

 his coadjutors on the dissociation curve, as modified by various agencies, is of 

 inestimable value. 



Before passing on to these important practical questions, it may be pointed out that it has 

 been shown that some colloidal solutions take up gases in greater proportion than is to be 

 accounted for by the increase of solubility with pressure. The experiments of Findlay (1908) 

 may be mentioned. Those of Geft'cken (1904) are also to the point. It may be asked why, 

 if the taking up of oxygen by haemoglobin is conditioned by a surface adsorption, other 

 colloidal constituents of the blood do not show a similar behaviour? Now, Geffcken's experi- 

 ments indicate a case which appears to be a typical one of adsorption, namely, that of carbon 

 dioxide by colloidal ferric hydroxide, but which is more or less "specific," in the sense that 

 oxygen is not taken up by the solution in any larger amount than by pure water. This system 

 of carbon dioxide and ferric hydroxide would repay further investigation, especially from the 

 point of view of reversibility. Granting that it is one of adsorption, we must remember that 

 this process is due to a diminution of surface energy of any kind, so that, as already pointed 

 out, chemical combination on the surface, if associated with diminution of surface energy, 

 would take place. But this does not really help us in the haemoglobin problem, because we 

 are still faced with the same difficulty of equilibrium with different oxygen tensions ; the 

 hypothetical chemical compound is merely changed in position, so to speak. Moreover, it is 

 not easy to see how a permanent equilibrium could be established, since the compound on the 

 surface must interchange sooner or later with the molecules inside the aggregate. Is it 

 possible that, after all, there may be some state of combination, neither mere surface adsorp- 

 tion nor chemical in the true sense, but intermediate between them, as appears to have been 

 held by van Bemmelen and by Ostwald? It might perhaps be related to surfaces of very 

 great curvature, as met with in colloidal systems, where reactions do not obey the simple laws 

 of mass action, nor, according to some, the phase rule. 



Relation to Temperature. Under a given oxygen pressure, it is found that less 

 oxygen is taken up by haemoglobin the higher the temperature. A series of 

 curves will be found in Fig. 190, from Barcroft's book (1914, p. 36). This is 

 clearly of importance with regard to the giving up of oxygen to the tissues. 

 Suppose that blood at 38 has come into equilibrium with an oxygen tension of 

 100 mm. of mercury in the alveolar air of the lungs. It will be 93 per cent, 

 saturated. From the experiments of Verzar (1912, 3), we find that the oxygen 



