204 HAEMOGLOBIN. 
able aggregations of the smaller crystals, exhibit, like aggregations of 
blood corpuscles, the red colour characteristic of the blood. 
We shall now examine successively the most important facts con- 
nected with the (1) form, (2) quantity of water of crystallisation, 
(3) solubility, presented by crystallised oxyhemoglobin, (4) diffusibility. 
1. Form. — (a) The blood of man and of the immense majority of 
animals yields oxyhemoglobin which crystallises in rhombic prisms or 
needles belonging to the rhombic system. 
(b) The oxyhemoglobin of the guinea-pig presents crystals which 
were described by Lehmaim as regular octohedra. They were, however, 
shown by the eminent crystallographer v. Lang 1 to be tetrahedra 
belonging to the rhombic system. 
The blood of certain birds,- and occasionally apparently of the 
rat 3 , i , 5 , yields crystals of the same form. 
(c) The oxyhemoglobin of the squirrel crystallises normally in the 
form of six-sided plates belonging, as proved by v. Lang, to the hexagonal 
system. These crystals had been first described by Lehmaim and Kunde. 
The blood of the hamster (Cricetus vulgaris) contains oxyhemoglobin 
which crystallises, as Lehmann showed, in rhombohedra and six-sided 
plates belonging to the hexagonal system. Halliburton, 6 who has studied 
the crystallography of oxyhemoglobin with great care, has made the 
interesting observation that "after recrystallising squirrel's hemoglobin 
several times the hexagonal constitution of the crystals is broken down, 
and the crystals obtained are either rhombic prisms or a mixture of 
these with rhombic tetrahedra." 
Rollett, 7 taking for granted that oxyhemoglobin, from whatever source 
obtained, possessed the same chemical composition, argued, from the fact of 
its crystallising generally in the rhombic, but hi the case of the squirrel in the 
hexagonal system, that oxyhemoglobin should be looked upon as dimorphous. 
Halliburton, however, with perfect correctness, hesitates to admit this 
view, which could only be held if we were certain that the haemoglobins whose 
crystals belong to different systems possess identical composition, and suggests 
that perhaps the difference in the crystalline form, as well as the difference in 
solubility of the haemoglobins which crystallise differently, depends upon 
varying quantities of water of crystallisation — that, in fact, the haemoglobins 
which crystallise in different systems represent " different hydrates of oxy- 
hemoglobin." s This may be the case, though it appears to me that the cause 
of the difference lies deeper. 
It has been previously stated — and the grounds for the statement will be 
given in a subsequent section — that, notwithstanding the perplexingly dis- 
cordant results of the analyses of oxyhemoglobin, there is, in the hemoglobin 
of all animals, absolute identity of the essential iron-containing nucleus, i.e. 
1 In a paper by A. Rollett, entitled "Versuche u. Beobachtungen am Blut, nebst 
krystallographisch. u. optiseb. Mittheilungen ueber die Blutkrystalle von v. Lang," 
Sitzungsb.d. k. Ahad. d. JVissensch., Wien, 1S62, Bd. xlvi. S. 66-98. 
2 Halliburton, "Text Book of Cbemical Physiology," London, 1891, S. 270. 
:: , 4 Kunde, Lehmann, see Preyer, "Die Blutkrystalle," S. 38. 
5 Hoppe-Seyler, "Ueber die Krystallformen der Blutkrystalle, " Med. Chew. Untersuch., 
Berlin, 1868, S. 195. 
""Preliminary Communication on the Haemoglobin Crystals of Rodents." Joum. 
Physiol., Cambridge and London, 1886, vol. vii. p. 2 ; Quart. Joum. Micr. Sc, London, 
vol. xxviii. p. 181. 
7 Loc cit. 
s Halliburton, "Text Book of Chemical Physiology," section on the "Crystallography of 
Oxyhemoglobin," pp. 270-274. The student is recommended to read this interesting and 
suggestive section. 
