PORPHYRINS 13 



heart — the relation of that body to haBmoglobin. Fox showed that 

 there was in addition to the oxy-body, the reduced body and the 

 body analogous to hsemochromogen, a complete series of haemoglobin 

 analogues. Moreover — and this is the point that matters — the differ- 

 ence between the haemoglobin bodies and the chlorocruorin bodies 

 is that the latter are built up on a different foundation of porphyrin 

 from the former. Whereas all forms of haemoglobin hitherto found 

 in nature are derivatives of protoporphyrin, chlorocruorin is a deriva- 

 tive of some other and as yet unknown member of the porphjrrin 

 series. 



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ChL 



orocruon,-n 



Horse ViaemogloblTi 



OxyViaemogloblTi from haemato- porphyrinic la 



Oxyhaemoqlobln from meso-porpViyrin J^lo! ^1/3 



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Fig. 1. (1) Position of a- and j8-bands of chlorocruorin (Fox). (2) Position of ,a- and 

 j3-bands of horse haemoglobin (Fox). (3) Position of a- and j8-bands of oxy- 

 haemoglobin made from hsematoporphyrin (Hill and Holden). (4) Position of 

 a- and j8-bands of oxyhaemoglobin made from mesoporphjTin (Hill and Holden). 



At this point I can claim to become a little reminiscent, for the 

 mention of strong sulphuric acid coupled with haematoporphyrin 

 carries me back in memory to the "old physiological laboratory," 

 the same in which Foster fired BaKour with a zeal for embryology; 

 to the room, on the opposite side of the passage from Foster's, in 

 which Hopkins isolated tryptophane and in which Laidlaw, under 

 his benign influence, made the following observation, namely, that 

 whilst the strongest possible reagents, such as concentrated H2SO4 , are 

 required for the dislodgement of the iron from oxyhaemoglobin, only 

 very weak acid is necessary for the formation of porphyrin from 

 reduced haemoglobin. In the case of Laidlaw's original observation 

 the blood was reduced by bacterial action, but he showed that there 

 was nothing specific about that; any form of reduction would serve. 

 For the moment I will pass over the great significance of Laidlaw's 

 observation as showing the intimate connection between the lability 

 of iron in haemoglobin and the oxygen and proceed directly to three 

 other observations of Laidlaw's (8) which are in the straight line of 

 our present enquiry: (1) that he could put back the iron and so 



