CHEMICAL BASIS OF THE ANIMAL BODY. 219 



in a short time its contents usually become almost pasty from the mass 

 of crystals which form in it. These are then centrifugalised off, dissolved 

 in a minimal amount of water, filtered, cooled to 0, and after the 

 addition of one quarter of its bulk of cooled alcohol again immersed in 

 a freezing mixture. The second crop of crystals thus obtained may be 

 again recrystallised as already described. The crystals are finally 

 washed with water at containing 25 p.c. of alcohol, and may be 

 dried in vacuo over sulphuric acid at 0, and are now fairly stable. 



The crystals obtained from the haemoglobin of various animals 

 differ in their crystalline form. The following figure shows some of 

 the most typical forms 1 . 



FIG. 35. CKYSTALS OF OXY-H^EMOGLOBIN. (After Funke.) 

 a. Squirrel, 6. Guinea-pig, c. Cat, or Dog, d. Man, e. Hamster. 



Apart from these differences in crystalline form the oxy-haemoglobin 

 of different animals varies in its solubility, in the amount of water of 

 crystallisation with which its crystals are united, and also apparently 

 in its percentage composition. The crystals are pleochroic but to a 

 less extent than are those of haemoglobin 2 . As against these differ- 

 ences it is important to notice that the close relationship of the 

 various forms of oxy-hsemoglobin from whatever blood they may be 

 obtained is shown by the fact that the spectroscopic properties are in 

 all cases identical, as also are the products of decomposition and the 

 compounds formed with gases. Numerous analyses of oxy-hsemoglobin 



1 For a discussion of the various crystalline forms of oxy-heemoglobin see 

 Halliburton, Chem. Physiol. and Pathol. 1891, p. 270. 



2 A. Ewald, loc. cit. (sub haemoglobin). 



