198 W. D. HALLIBURTON. 



minerals, namely, differences of temperature and of solvent, have 

 in the case of haemoglobin no influence. 



If we then fall back on the latter alternative, the question 

 which arises is whether there are any facts to support it. The 

 explanation that the varying form of oxyhemoglobin is due to 

 varying quantities of water of crystallisation may be other- 

 wise expressed by saying that we have to deal with different 

 hydrates of oxy haemoglobin. This would account for the 

 varying solubilities of these substances in water and other 

 reagents, and at the same time is not such an essential differ- 

 ence as to prevent the chief properties of hsemoglobin from 

 being universally the same. 



Turning to Hoppe-Seyler's researches on this subject of water 

 of crystallisation, it is seen that its amount varies consider- 

 ably. The following is his table -} 



Percentage of Water of Crystallisation. 



Dog's haemoglobin 3 to 4 



Guinea-pig's ...... 7 



Squirrel's ,,..... 9 - 4 



Goose's „ O'i 



In an earlier paper, 2 the same author gives rather different 

 percentages, viz. for guinea-pig's hsemoglobin 6, for goose's 

 hsemoglobin 7, and for squirrel's hsemoglobin 9. Dr. Christian 

 Bohr 3 has more recently made observations on the water of 

 crystallisation of dog's hsemoglobin, and as the result of 

 thirteen experiments he finds that its amount varies from 6*3 

 to 12 per cent. It is thus seen that great variations occur in 

 the numbers obtained by these experiments. The reason for 

 this variation seems to me to be the great difficulty of obtain- 

 ing hsemoglobin in a pure state, and also possibly because the 

 method adopted, which is the same as that carried out in 

 similar investigations on inorganic salts, is not applicable to 

 such a complex and much less stable organic compound as 



1 'Physiologische Chemie,' p. 377. 



2 ' Med. Chem. Untersuchungen/ Heft iii, 1868, p. 370. 



% ' Experimental Untersuchungen iiber die Sauerstoffaufnahme des Blut- 

 farbstoffes,' Kopenhagen (Olsen and Co.), 1885. 



