50 HEMOGLOBIN 



or S-shaped curves might easily appear straight; but it seems diffi- 

 cult to doubt that a relation of some sort exists. 



The importance of such a relationship appears when some attempt 

 is made to assign a reason either for the variability of the span, or 

 the variability of K, for if the span and K bear any simple relation 

 to one another it would follow that a cause which alters one alters 

 both. 



The most natural opening to the problem of the variation in the 

 span is to ask : Is it due to some disparity in the haematins of the various 

 haemoglobins or to the proteins? To this question an answer can 

 be attempted. By reduction in alkaline solution the globins may be 

 denatured and the corresponding haemochromogens produced. There 

 is no measurable difference in the positions of the haemochromogen 

 bands, even though the haemoglobins from which the haemochromo- 

 gens were made differ spectroscopically(7). Of course if we go into 

 the larger world of haemochromogens made by the attachment of 

 pyridine, nicotine, etc. to haematin we do get differences, the haemo- 

 chromogen bands are shifted a little one way or the other, but the 

 spectra of haemochromogens built on a basis of denatured globin are 

 all the same (13). It would appear therefore that the denaturation 

 of the globin reduced all haemoglobin spectra to a common level, and 

 that would go to show that the specific differences in the spectra 

 of different vertebrate bloods found an explanation in the properties 

 of the undenatured globin present. 



If it be then that the span is related to the gas-bearing properties 

 of haemoglobin we are brought to believe that the fine adjustment, 

 so far as these properties are concerned, rests in the globin portion of 

 the molecule, and that human blood has a different affinity for oxygen 

 to frog's blood, not because its haemoglobin is built upon a different 

 basis of porphjrrin, but because its porphyrin is attached to a different 

 globin. And what is true of the affinity for oxygen would be true of 

 the temperature coefficient of the same, and this truth would confer 

 on globin a definite role in the evolution of the animal kingdom. 



