190 W. D. HALLIBURTON. 



gether with the ordinary rhombic prisms and plates. In 

 order to verify this, I have made numerous specimens of the 

 crystals from the blood of about fifteen rats. As a rule, no 

 hexagons were present ; but on three occasions I have detected 

 hexagonal plates — very few in number, perhaps not more than 

 one or two on the slide — among the rhombic crystals. There 

 appeared to be nothing special either about the animal used 

 or the method employed in these cases. The diameter of 

 these crystals averaged about the same as in squirrel's blood 

 (002 — "003 m.). Between crossed nicols they also behaved 

 the same as squirrels' haemoglobin crystals, viz. remained dark 

 in all positions. 



In addition to this, if crystallisation be watched under the 

 microscope, a single corpuscle will often be observed to set 

 into a minute hexagon. This is what Preyer calls intraglobular 

 crystallisation. He describes it as occurring in the blood of 

 the hamster. It can also be observed in the blood of the 

 rat. The crystals apparently so formed last but a few seconds, 

 the corpuscles then becoming shrunken, or irregular, and very 

 often under the subsequent action of water, globular. It is 

 therefore possibly a stage in the crenation of the corpuscle. 

 But, apart from this, it is undoubtedly the fact that hexagonal 

 crystals are occasionally found in the blood of the rat. 1 It 



1 Since writing the above, I have received the following in a letter frofn Mr. 

 Sheridan Lea, of Cambridge. He says : — " When I was showing a class how 

 to put up permanent specimens of haemoglobin crystals from rat's blood, we 

 obtained uniformly hexagons, instead of prisms. This I have neither ever 

 noticed or heard of before, and I thought it might be of interest to you. 

 The method employed was that of Stein (' Centralb. f. d. med. Wiss.,' 1884, 

 No. 23, and ' Virchow's Archiv,' 97, 483)." I had myself occasionally used 

 Stein's method of preparing crystals from rat's blood, but had always obtained 

 the usual rhombic prisms. On receiving Mr. Lea's letter I made a large 

 number of preparations of haemoglobin crystals by this method. The method 

 consists in simply mounting a drop of defibrinated blood in a drop of Canada 

 balsam. In the case of some animals, among which were man and the mouse, 

 I was not able to get any crystals at all. In the commoner mammals, dog 

 and cat, the crystals obtained were very fine specimens of rhombic prisms. 

 In the guinea-pig and squirrel they presented the usual tetrahedral and 

 hexagonal shapes respectively. With rat's blood, however, the results were 



