82 H. C. SORBY. 



stituent of these two modifications of haemoglobin. If this be 

 so, we might reasonably expect to find some difference in 

 their chemical relationships, whilst at the same time both 

 might yield identical coloured products. This is most cer- 

 tainly the case. When treated with citric acid both yield the 

 same hsematin, but the haemoglobin of human blood is far 

 less stable and far more easily decomposed than that from 

 Planorbis. Taking an equal quantity of both, and adding an 

 equally small quantity of citric acid, the haemoglobin of human 

 blood was changed almost at once into hsematin, whereas 

 that from Planorbis showed no such sudden decomposition ; 

 and even after half an hour was not so much changed as the 

 other in less than a minute. In another experiment, taking 

 equal quantities of the tAvo haemoglobins, I added twice as 

 much citric acid to the Planorbis. That of human blood was 

 changed to haematin and lost the haemoglobin bands in ten 

 minutes, whereas that from Planorbis was changed so much 

 more slowly that the alteration was not complete until after 

 two hours, though, as I have said, the amount of citric acid 

 was double. Hence clearly enough the haemoglobin of 

 Planorbis is a far more stable compound. I am also much 

 inclined to believe that some of the secondary spectra do 

 also differ in important characters. Thus, when the haemo- 

 globin of Planorbis was deoxidized, I could see a faint 

 absorption band at about wave-length 504, not visible in the 

 case of deoxidized human heemoglobin. This may be due to 

 some other colouring matter mixed with the original, but the 

 sj)ectrum of the oxidized compound furnishes no evidence of 

 any such second substance. Taking everything into con- 

 sideration, it appears to me that the complete study of these 

 two modifications of haemoglobin cannot fail to thrOAv very 

 much light on a number of interesting physical and bio- 

 logical questions. It also appears to me very desirable that 

 the haemoglobin of the various animals in which it has been 

 detected by Hay Lankester and others should be carefully 

 examined from this new point of view, in order to ascertain 

 whether the tAvo modifications are correlated to the existence 

 or non-existence of blood discs, since perhaps it may be 

 found that the modification of globulin met Avith in Planorbis 

 is characteristic of blood coloured by a haemoglobin solution, 

 and the other modification that Avhich is essential to the forma- 

 tion of coloured blood discs in a nearly colourless serum. 



According to the observations of Ray Lankester,^ there is 

 strong reason to believe that haematin is the coloured radical 

 of his chlorocruorin, which plays the part of haemoglobin in 

 ' ' Journal of Anatomy and Physiology,' vol. iv, p. 125. 



