4 HEMOGLOBIN 



its danger as a poison, the current view being that CO itself is in- 

 nocuous, but that uniting with the haemoglobin of the body it prevents 

 the carriage of the oxygen, necessary for life, to. the brain and other 

 organs. It might be inferred that to forms of life which did not depend 

 on haemoglobin for their oxygen supply, carbon monoxide would 

 be harmless. Yet this is not the case. Warburg(20) has shown that CO 

 inhibits the oxygen uptake of yeast and J. B. S. Haldane(2i) that both 

 to growing seedlings and to moths carbon monoxide is poisonous even 

 though these forms of life are devoid of haemoglobin. Moreover, 

 the poisonous dose does not depend upon the absolute amount of 

 carbon monoxide present but on its concentration relative to that 

 of oxygen. 



The union of carbon monoxide in such small concentrations with 

 haemoglobin has been analysed by Hartridge and Roughton(22). The 

 equilibrium constant of each of the reactions 



CO + Hb :^ COHb 

 and O2 + Hb 5^ OgHb 



is of course the quotient of the velocity constants of the two phases 

 of the reaction. Hartridge and Roughton, by extraordinarily in- 

 genious methods, have measured the four velocity constants involved, 

 and found that the great affinity of CO for haemoglobin is due not to 

 the great magnitude of the velocity constant for the phase 



CO 4- Hb — COHb, 



but to the small value of the constant for 



CO + Hb -«— COHb. 



The equation 



CO -h Hb = COHb, 



written in that way, expresses a heritage of convention, for the 

 molecular weight of haemoglobin has at last been determined in 

 two quite different ways independently by two observers. By a 

 curious irony one of these methods depends upon its extreme slowness, 

 the other on its extreme speed. Adair (23), by measurements of the 

 osmotic pressure, each measurement extending over months, has 

 found the osmotic pressure over a great range of conditions to cor- 

 respond to about 70,000. This figure is the same as that more recently 

 obtained by Svedberg(24), who, spinning solutions of haemoglobin 

 at about 10,000 revolutions per minute, actually concentrated the 



