THE WATER OF CRYSTALLISATION. 
205 
of that moiety «»f the molecule on which its colour and its physiological func- 
tion depends. At the same time, there is such a difference in the ratio of 
S:Fe in the haemoglobin of certain animals as renders it highly probable, or 
rather certain, that, in the haemoglobin of different animal groups, the albu- 
minous moiety of the complex molecule differs. Such heing the case, it is not 
surprising that certain of the physical characters of haemoglobin, such as 
crystalline form and solubility, should exhibit variations. 1 Nor can we lose 
sight of the possibility, to which I have already drawn attention, that the 
differences in the haemoglobins of certain animals may be due to their being 
formed by the linking of the iron-containing molecule with different polymers 
of the same albuminous group. The existence of haemoglobins varying some- 
what in their percentage of iron renders this view highly probable. 
2. Quantity of water of crystallisation. — Eemarkable difficulties 
encounter the observer in his attempts to determine the amount of 
water of crystallisation of oxyhemoglobin, and considerable discrepancies 
are to be noticed in the results obtained by different processes. 
In order to make the determination, pure oxyhemoglobin is dried 
in vacuo at 0° C, and after ceasing to lose weight under these conditions 
it is heated to a temperature of 115 C. 
The following are some of the principal and most reliable results 
obtained : — 
Oxyhemoglobin. 
Water of 
Crystallisation 
per cent. 
Authority. 
Dog 
Horse .... 
Pig 
Guinea-pig 
Squirrel .... 
3*4 Hoppe-Seyler. 
3-94 Hufner. 
5-9 Otto. 
6 Hoppe-Seyler. 
9 Hoppe-Seyler. 
According to Bohr, 2 the water of crystallisation of oxyhemoglobin may 
vary in amount between 1*2 and 6'3 per cent., but these results, like others 
obtained by the same author, and to which reference has been made (see p. 
192), are explicable by the fact that his preparations of haemoglobin did not 
represent the pure substance, and contained products of decomposition. 
Without taking Bohr's results into consideration, there can be no 
doubt that crystals of oxyhemoglobin of different animals exhibit 
differences in the amount of water of crystallisation. Assuming the 
above results to be correct, the highly soluble oxyhemoglobin of the 
pig, which crystallises in rhombic prisms, possesses the same amoimt of 
water of crystallisation as the very sparingly soluble oxyhemoglobin of 
the guinea-pig, separating in the form of tetrahedra. 
3. Solubility. — The difficulties which encounter the observer in 
1 The reader is referred to an admirable account of all the researches on the Crystal- 
lography of Haemoglobin, up to the date of its publication (1871), to the chapter entitled 
" Krystallformen des Blutroths," in Preyer's work, "Die Blutkrystalle." Very fine 
coloured engravings of the haemoglobin crystals of various animals — amongst others, of 
man, the guinea-pig, and the squirrel — are to be seen in Funke's "Atlas of Physiological 
Chemistry," being a Supplement to Lehmann's "Physiological Chemistry, London, 
printed for the Cavendish Society, 1853. See plate x. and ppl 15-17 of the appended 
letterpress. 
2 "Exp. Untersuchungen u. die Sauerstoffaufnahme des Blutfarbstoffes. '' Copenhagen 
1885. 
