HEMOGLOBIN CRYSTALS OF RODENTS' BLOOD. 187 



to find that their minute size, and especially their extreme 

 tenuity, prevents our applying the crucial test of the inter- 

 ference figures seen in convergent polarised light. 



' f Bertrand devised a form of microscope which enables these 

 interference figures to be studied in the minute crystals seen 

 in their rock sections, and von Lasaulx has improved this 

 apparatus. We have what I believe to be the best form of the 

 Bertrand-Lasaulx apparatus constructed by Nachet; but even 

 employing an immersion objective magnifying 650 diameters, 

 the crystals are still so small as to give neither rings, nor cross, 

 nor brushes. 



" I greatly regret that we have not been able to apply this 

 test. I fear that no instrument exists which will accomplish 

 what you desire ; and Mr. Fletcher, on theoretical grounds, 

 doubts whether it would be possible under any conditions to 

 apply the test to such minute crystals." 



The largest crystals of squirrel's haemoglobin that I have 

 obtained were those formed by the addition of water to the 

 defibrinated blood; they varied in size from "001 to *005 m. in 

 breadth. 



Since receiving Professor Judd's report, I have tried to 

 obtain larger crystals by Gscheidlen's 1 method. He seals 

 defibrinated blood in narrow glass tubes, which are then kept 

 at a temperature of 37° C. for several days. On opening these 

 tubes and emptying their contents into a watch glass, crystals 

 of great size are formed from dog's blood after evaporation has 

 occurred. 



With squirrels' blood, however, I have not obtained larger 

 crystals by this method than by the first. The reason for this 

 seems to be the extreme readiness with which squirrels' haemo- 

 globin crystallises. It is a well-known fact that bodies that 

 crystalise rapidly crystallise in small and numerous crystals. 

 If some method could be devised for retarding, but not pre- 

 venting, the crystallisation of squirrel's haemoglobin, we might 

 then be able to obtain crystals of it large enough to which to 

 apply this crucial test. 



1 ' Physiologische Methodik,' p. 361. 



