CHEMICAL CONSTITUTION OF THE RED CORPUSCLES. 413 



crystalline systems. Lang* was the first to show that what 

 were regarded as regular tetrahedra from the blood of the 

 guinea-pig, when examined with a Nicol's prism in a polarising 

 microscope, appeared clear in four azimuths, and dark in four 

 azimuths, and therefore that from their optical characters they 

 belonged to the rhombic system : and further, that when com- 

 pared with the prismatic crystals of human blood belong- 

 ing to the same system, the following results were obtained. 

 The lengths of the axes of the prisms of human blood present, 

 according to measurements of the acute angle of the rhombic 

 terminal plane (54 1'), the proportion of 1 : 1,96 = 1 : 2 "0,98; if 

 then the second axis-length be divided by 2, the two axes would 

 be of nearly equal length, which agrees well with the crystals 

 from the blood of the guinea-pig. 



The crystals of by far the greatest number of animals, how- 

 ever, occur either in the form of simple tetrahedra, or of tetra- 

 hedra with truncated angles and edges ; or, like those of man, 

 they form rhombic prisms, respecting which the recent treatise 

 of Prey erf may be consulted. The blood crystals of squirrels 

 alone, formerly described as six-sided plates, appear, as shown 

 by Von Lang,f to be six-sided plates belonging to the hexagonal 

 system. 



Yon Lang also first demonstrated that crystals of haemoglobin, 

 examined in two azimuths, with only one Nicol's prism over or 

 under the object, exhibited colours different from those in the 

 two intervening ones, and that they therefore present absorption 

 phenomena in regard to light, in accordance with their crystal- 

 line form (Pleochroismus). 



Besides haemoglobin, a series of other substances have been 

 ascribed to the blood corpuscles, constituting their colourless 

 portion, which nevertheless appear to exist in very variable 

 quantities in different animals. To these belong the albuminous 

 bodies. The globulin, or paraglobulin of Kiihne may be pre- 

 cipitated by means of carbonic acid from blood corpuscles mo- 



* Sitzungsberichte der Wiener Akademie, Band xlvi., p. 85, et seq. 

 t Pfliiger's Archiv, Jahrgang, 1868, p. 365. 

 1 Loc. cit., p. 89. 



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