THE UNION OF OXYGEN WITH HEMOGLOBIN 119 



is definitely not a parabolic one as is attested by the multitude 

 of dissociation curves which have been determined. Of these, most 

 present definitely a double inflection, some appear not to do so, but 

 none is of the shape depicted by Ostwald. One is tempted to ask 

 why he should ever have pubhshed curves which appear to be so 

 widely divorced from experimental truth. The reason is simple 

 enough: at the time when Ostwald's paper was written there was 

 very Httle exact knowledge as to the shape of the oxygen dissocia- 

 tion curve. 



The contention that haemoglobin can unite with an indefinitely 

 large quantity of oxygen appears also to be contrary to the facts as 

 determined experimentally. The same is true of carbon monoxide. 

 If blood is brought into equihbrium with oxygen in the cold at 

 atmospheric pressure, the haemoglobin will not absorb an appreciably 

 greater quantity of oxygen even if exposed to an atmosphere of pure 

 oxygen gas. The dissociation curve has become asymptotic. 



The same thing has been shown with regard to the affinity of 

 carbon monoxide for haemoglobin, and in this case the demonstration 

 is much more striking than in the case of oxygen because, owing to 

 the fact that haemoglobin has some 250^ times as great an affinity 

 for carbon monoxide as for oxygen, the curve becomes asymptotic 

 at a very much lower pressure. The proof that there is a definite 

 limit for the amount of carbon monoxide with which a given quantity 

 of haemoglobin will unite was shown in a very elegant way by 

 W. E. L. Brown (2). 



It is not merely that the union of oxygen and haemoglobin obeys 

 the law of definite proportions, but also that it obeys the law of 

 simple proportions, as has been shown in the chapter on its specific 

 oxygen capacity. It may be pointed out further that the quantity 

 of oxygen with which haemoglobin unites, namely, one gram molecular 

 weight of oxygen to 17,000 grams of haemoglobin, offers a conception 

 very different from that which one ordinarily has with regard to 

 adsorption, the latter conception being that of a large molecule with 

 numerous small molecules adhering to its surface and having no 

 particular preference for any one portion of the surface rather 

 than another. In the case of haemoglobin the 17,000-gram molecular 

 unit unites with but one gram molecular weight of oxygen, 

 and further this molecule attaches itseK to a perfectly definite 

 portion of the haemoglobin molecule, namely, the haematin, and 

 ^ Sheep's blood at room temperature. 



