352 



RESPIRATION. 



[FIG. 94. 



a mass of crystals. The crystals may be separated by filtration, redissolved in water, 

 and recrystallized. 



Hemoglobin from the blood of the rat, guinea-pig, squirrel, hedgehog, 

 horse, cat, dog, goose, and some other animals, crystallizes readily, the crys- 

 tals being generally slender, four-sided prisms belonging to the rhombic 



system and often appearing quite 

 acicular. [Figs. 94, 95, 96.] The 

 crystals from the blood of the guinea- 

 pig are octahedral, but also belong to 

 the rhombic system ; those of the 

 squirrel are six-sided plates. The 

 blood of the ox, sheep, rabbit, pig, 

 and man crystallizes with difficulty. 

 Why these differences exist is not 

 known ; but the composition and the 

 amount of water of crystallization 

 vary somewhat in the crystals ob- 

 tained from different animals. In 

 the dog the percentage composition 

 of the crystals has been determined 

 as C. 53.85, H. 7.32, N. 16.17, O. 

 21.84, S. 0.39, Fe. 0.43, with 3 to 4 

 per cent, of water of crystallization. 

 Tetrahedral from Blood of the Pig.] J t w j}} t h ug b e geen that hsemoglo- 



bin contains, in addition to the other 



elements usually present in proteid substances, a certain amount of iron ; 

 that is to say, the element iron is a distinct part of the haemoglobin 



aBaa**"* 



.1 - A fl V*!^ _*. .* 



T v v.. 



[FIG. 95. 



[Fio. 96. 



Hexagonal Crystals from Blood of Squirrel. 

 On these six-sided plates, prismatic crystals, 

 grouped in a stellate manner, not infrequently 

 occur. (After Funke)]. 



Prismatic, from Human Blood.] 



molecule, a fact which of itself renders haemoglobin remarkable among the 

 chemical substances present in the animal body. 



288. The crystals when seen in a sufficiently thick layer under the 

 microscope have the same bright scarlet color as arterial blood has to the 

 naked eye ; when seen in a mass they naturally appear darker. An aqueous 

 solution of haemoglobin, obtained by dissolving purified crystals in distilled 



