192 HEMOGLOBIN 



bodies of the conjugated protein type? or again, if one takes the two 

 moieties of the conjugated protein — Are there bodies from which one 

 can suppose that they have been derived? Along the Une of the 

 protein we are lost at once. I suppose there is no form of animal life 

 but contains some protein to which C34H3Q04N4FeOH might not 

 conceivably attach itself. Along the line of the pigment we have 

 to consider what substances may have been the precursors of 

 C34H3o04N4FeOH. 



There has not lacked speculation on this subject, and a number of 

 obvious materials present themselves for our consideration. Of these 

 mention may first be made of the porphyrins. It is a commonplace 

 that a large literature has grown up around these substances within 

 the last few years. At present one can only say that there are quite 

 a number of cases which might be cited in which porphyrins occur 

 in animal tissues — the dorsal Hne on the back of the earthworm, 

 the pigment of the hen's egg-shell, and the pigment laid down in the 

 bones and teeth of cases of hsematoporphyrinuria ; to say nothing 

 of the kindred bile pigments; but it cannot be said of any of these 

 that they are a stage on the up-grade to haemoglobin, or indeed that 

 they are ever made in the body out of anything but haemoglobin. 

 Certainly bile pigments and the pigment of the egg-shell are degrada- 

 tion products ; of the other two cases cited we know nothing one way 

 or the other. It has been pointed out to me by Sir Frederick Hopkins, 

 that an attractive analogy might be drawn between porphyrinuria 

 and other complaints, such as cystinuria and alcaptanuria, and that 

 these substances appear to be produced as the result of the stoppage 

 of a synthetic process ; but this is at best only an analogy, and it has 

 not been suggested that the analogy could be driven home. 



The porphyrins are of two main classes. It is a httle remarkable 

 that hsematoporphyrin, the form of porphyrin which is obtained in 

 haematoporphyrinuria, is not that which might be expected to occur 

 as a stage in the formation of haemoglobin: that would be proto- 

 porphyrin, the form found in the egg-shell is a direct derivative of 

 haemoglobin. 



In our discussion we have left over the finer points of the globin 

 influence. At the point at which we left the matter we had said that 

 the globins in the various haemochromogens of which haemoglobin 

 is made were so nearly the same that spectroscopically they cannot 

 be separated. Nevertheless different haemoglobins differ greatly. It 

 is rather for future research to discover the precise biological signi- 



