184 W. D. HALLIBURTON. 



My own observations are as follows : — The crystals can be 

 obtained with the greatest ease by simply adding a drop of 

 water to a drop of defibrinated blood on a slide, and covering 

 it ; in less than a minute crystals appear. I have also prepared 

 them by other methods ; l but in all cases the crystalline form 

 is the same. When first formed the crystals are six-sided 

 plates, many equilateral, but many not. After recrystallisation, 

 however, the crystals are then all but perfectly regular. The 

 quetions then arises, Do they belong to the hexagonal system or 

 not ? To this question one of the three following answers must 

 be the correct one. 



1. They do belong to the hexagonal system. 



2. They do not belong to the hexagonal system, but are 

 rhombic crystals, having a so-called "hexagonal habit." In 

 mineralogy instances are known of such occurrences. This is 

 the case with copper-glance, some of whose crystals so closely 

 resemble hexagonal ones that several mineralogists believed 

 that there were two kinds, one being hexagonal. Again, mica 

 is an instance of a monoclinic crystal with " hexagonal 

 habit." 



Fig. 2. Fig. 3. 



Suppose a b c d (fig. 1) to be the basal plane of a rhombic 

 plate, and the angle a b c to be approximately 120°, the lines 



1 The method that I have found best for the preparation of blood-crystals 

 in most animals is to add to defibrinated blood a sixteenth of its volume of 

 ether, and then to shake for two or three minutes until the liquid becomes of 

 a clear lake colour; in the course of time, varying from five minutes to three 

 days, crystals form in abundance (' Gamgee's Physiological Chemistry,' p. 87) 



