HJ1M0GL0BIN CRYSTALS OF RODENTS' BLOOD. 191 



would therefore be possible that such crystals occasionally may 

 occur in the blood of other animals, such as the mouse, the 

 usual form of whose blood-crystals is, however, rhombic. 



The rats employed in the above experiments were the 

 common house rat, and also tame rats. 



3. Influence of the other Constituents of the Blood on the 

 Crystalline form of Haemoglobin Crystals. 



These experiments, as well as those in the next section of 

 this paper, were undertaken at the suggestion of Professor 

 Schafer. 



The blood-crystals of an animal have the same form whether 

 they be obtained from the fresh blood, or from the blood from 

 which the fibrin has been removed. Fibrin, or its precursor 

 in the blood-plasma fibrinogen, has then no influence on the 

 form of the blood-crystals. 



The following experiments were undertaken to ascertain 

 whether the other constituents of the blood-plasma, which are 

 all contained in the serum, have any effect in influencing the 

 form of the crystals. 



The method of experimentation was as follows: — Defibrinated 

 blood is taken in a tube and centrifugalised for about half an 



very strange. In the majority of cases the usual rhombic needles were formed ; 

 but in a few cases I confirmed Mr. Lea's observations, and obtained perfectly 

 regular hexagons ; in some cases the hexagons would occupy one part of the 

 slide only, while the remainder was filled with the ordinary prisms. Hexagons 

 seemed to form where the proportion of blood to balsam was small, and they 

 were formed especially at the edges of a preparation where the drop of blood 

 had probably had time to dry somewhat before being covered with Canada 

 balsam. These hexagons remained dark in the dark field of the polarising 

 microscope. After a day or two they cracked in a peculiar way, and seemed 

 then to be made up of minute needles radiating from a centre. This may or 

 may not indicate the way in which they are formed. The fact that they 

 occurred most in parts of the field where there was least water seems, how- 

 ever, to confirm the theory advanced later in the paper, viz. that the difference 

 of crystalline forms in haemoglobin is due to different amounts of water of 

 crystallisation. 



