26 



THE BLOOD. 



Fis. 14. 



Ni5p Fgj, Sg, O354. It may be obtained in quantity and tolerably 

 pure by the following method (Preyer) : 



Blood (preferably from a dog-) is di-awn into a capsule, and the seram allowed 

 to separate. The clot is then taken, and after being quickly minced, is thrown 

 upon a filter, and washed with ice-cold distilled water until the washings yield 

 but little precipitate with perchloride of mercmy. By this process the senim, 

 with the albumin it contains, is in great part removed, the cold water taking up 

 but little of the ha3moglobin. The latter is then dissolved out by wai-m water, 

 and an amount of alcohol, just insufficient to cause its precipitation, is added to 

 the solution. On placing this in a freezing mixtui'e, a large part of the hffimo- 

 globin crystallizes out. 



The crystals of hseraoglobin present various forms in different 

 animals, but ahnost all (the hexagonal plates of the squirrel alone 



being excepted) belong to the 

 rhombic system. From liuman 

 blood and that of most mam- 

 mals, the crystals are elongated 

 prisms (fig. 14, 1), but tetrahe- 

 drons in the guinea-pig (2), 

 and short rhombohedrons in 

 the hamster (4). They are 

 most readily obtained for mi- 

 croscopical examination from 

 the l)lood of the rat, where 

 they appear merely on the 

 addition of a little water. 



All haemoglobin crystals con- 

 tain a certain amount of water 

 of crystallization (Kiihne). 

 Tliey arc doubly refracting 

 (anisotropous), and the spec- 

 irum of haemoglobin, whether 

 in substance or in solution, 

 may be always readily recog- 

 nised by the double or single 

 absorption bands, which are 

 produced according as it is 



Fig. 14. — Blood-Ckystals, magnified. 

 1, from human blood ; 2, from the guinea- 

 pig ; 3, squirrel ; 4, hamster. 



present hi the oxidated or deoxidated condition.* 



Products of Decomposition of Haemogrlobin.— Hajmoglobin is an exceed- 

 ingly unstable body. Even at the ordinary temperature the crystals cannot 

 long be preseiwed without undergoing alteration, the substance of which 

 they are composed readily decomposing into an exceedingly pure (ash-free) 

 albuminoid substance, named by Preyer (jlolnn, and a brownish-red powder, 

 veiy nearly allied to hasmoglobin in chemical composition (hence teiined 

 'meffunnorjl(ihin), \mt differing from that body both in its general reactions and 

 in the character of its spectrum. Another brownish-red substance, which contains 

 all the iron of hemoglobin, and was long supposed to be the true coloming 



* For an account of the examination of the colouring matter of the blood by the prism, 

 and of the differences in its absorjitive effect on light, the reader is referred to an im- 

 portant paper by Professor G. Gr. Stokes, in the Proceedings of the Koyal Society for 

 June 16, 1864, vol. xiii.-p. 3.^.5, as well as to an exiiaustive treatise on the whole subject 

 of hajmoglobin, by W. Preyer (Die Blutkrystalie, Jena, 1871). 



