H^MOaLOBIN CRYSTALS OP RODENTS' BLOOD. 183 



occurs, vertebrate and invertebrate, crystals of it can be 

 obtained in the form of prisms and plates belonging to the 

 rhombic system. 



b. The exceptions to this rule hitherto noted are the 

 following : 



i. Guinea-pig. Haemoglobin crystals from the blood of this 

 animal are tetrahedra, once supposed to belong to the regular 

 system, but now shown by von Lang to be in reality rhombic. 



ii. Lehmann mentions that similar tetrahedra may be ob- 

 tained from the blood of the mouse and rat. This has not 

 since been confirmed. 



iii. In several birds the crystals obtained are also tetrahedra. 



iv. In three animals — the squirrel, the hamster, and the 

 mouse — six-sided plates have been described. 



v. In one of these, the hamster, rhombohedra are described 

 as occurring also. 



2. Hexagonal Blood-crystals. 



We will take the three animals in which the haemoglobin is 

 said to crystallise in the hexagonal form one by one. 



a. Squirrel. — The discovery of the fact that haemoglobin 

 crystals from this animal are six-sided plates was made by 

 Kunde (1852). Writing in the same year, Lehmann asserts 

 that though these crystals are six-sided they do not belong to 

 the hexagonal system. He gives, however, no reasons for this 

 assertion. Lang and Preyer arrived at the opposite conclusion 

 i. e. that they do belong to the hexagonal system, from the study 

 of their optical properties. 



Belideus breviceps (a marsupial). — Crystals similar to those of the 

 opossum. 



Seal (Phoca vituliua). — Rhombic prisms, many of them very short 

 and simulating hexagons. Easily obtained. 



Bear (Ursus syriacus). — Bunches of rhombic needles, easily obtained. 

 They are slenderer than those obtained from dog's blood as a rule, some being 

 almost silken in appearance. 



Hydromys leucogaster (white-bellied beaver rat). — Rhombic prisms. 



Sus leucomystax (white-whiskered swine). — Rhombic prisms. 



Water-vole (Arvicola aquatica). — Crystals are obtained easily by 

 adding water to the blood. They are of the usual rhombic shape. 



