232 MANUAL OF PHYSIOLOGY. 



The readiness with which the oxyhcemoglobi?i crystals are formed 

 varies much in different animals and under different circum- 

 stances, as may be seen from the following list : 



Most readily guinea pig, rat, mouse. 

 Readily cat, dog, horse, man, ape, rabbit. 

 With difficulty sheep, cow, pig. 

 Not at all frog. 



The presence of oxygen causes the crystals to form more rapidly, 

 so that a stream of oxygen passed through a strong solution of 

 haemoglobin causes small crystals of oxyhsemoglobin to form. 



The crystals always belong to the rhombic system, being most 

 commonly plates (man, etc.) and prisms (cat), and rarely tetra- 

 hedra (guinea pig) and hexagonal plates (squirrel). 



FIG. 106. 



Crystals of Haemoglobin from different animals, showing the variety in form 

 of crystals 1, guinea pig; 2, man; 3, squirrel. 



The color of the crystals and their solution vary according to 

 the light by which they are looked at. By reflected light they 

 are bluish-red or greenish in color, and by direct light scarlet. 



The preparation of oxyhcemoglobin crystals is accomplished by 

 first separating the coloring matter from the corpuscles by freezing, 

 or the addition of water or ether, and rendering it less soluble by 

 evaporation, cold, and the addition of alcohol. 



For microscopic observation it generally suffices to kill a rat 

 with ether, and expose a drop of the blood diluted with distilled 

 water on a slide until half dried, and then cover. Crystals ap- 

 pear in the fluid as it becomes more concentrated. 



