240 CRYSTALLOGRAPHY OF HEMOGLOBINS OF THE RODENTIA. 



GUINEA-PIG, A DOMESTICATED VARIETY OF Cavia cutleri. Plates 57 and 58. 



The blood of the guinea-pig is so easy to procure and to crystallize, 

 that it has been studied very carefully. Our specimens were obtained by 

 bleeding the live animals in the laboratory, and were always, therefore, 

 fresh blood. Many variations of the method of preparation were tried to 

 see if such variations produced any change or modification of the crystals. 

 The ordinary methods of preparation were usually followed in preparing 

 crystals for crystallographic study. The whole blood, oxalated, was laked 

 with ether and centrifugalized to obtain a clear solution, from which the 

 slide preparations were made. In such a solution crystallization is very 

 rapid, and the crystals are apt to be small. Diluting the blood with plasma 

 from the same blood was tried, with the result that the crystals were in- 

 creased in size, while remaining very perfect. In some cases, the blood 

 (defibrinated by beating without the addition of oxalate) was thus diluted 

 with the plasma of another portion of the sample that had been oxalated 

 to prevent clotting; and from this, also, veiy large and perfect crystals 

 were obtained. In the diluted blood, when the crystals grow to large size, 

 there is generally more tendency to form twins than in the undiluted blood. 

 To see whether the addition of certain inorganic salts had any effect upon 

 the form of the crystals, preparations were made from the same specimen 

 of blood (defibrinated by beating and laked with ether) as follows : 



(1) By the usual method of adding ammonium oxalate: In this case crystals 

 formed very rapidly, a pellicle of crystals appearing on the drop on the slide before the 

 cover was applied. The separation of the oxyhemoglobin was so complete that the 

 solution became colorless. Twins formed only sparingly. 



(2) Substituting potassium oxalate for ammonium oxalate: The pellicle of crystals 

 did not form on the drop, but crystallization proceeded until the solution was nearly 

 colorless. The crystals showed a tendency to form twins and irregular aggregates, 

 otherwise they were like the normal type. 



(3) Substituting sodium oxalate for ammonium oxalate: Crystallization was 

 slower than in cases (1) and (2), but the crystals were larger and more perfectly formed 

 than with either of the other oxalates. Twins were very plentiful. 



(4) Sodium chloride substituted for oxalate: This greatly retarded the crystalliza- 

 tion, but the crystals that formed were very large, relatively enormous. The crystals 

 did not show much tendency to twin. 



(5) Substituting calcium chloride for an oxalate: This retarded the crystallization, 

 as in the case of the addition of sodium chloride; but the crystals were more numerous, 

 and not nearly so large as those obtained by method (4) . 



In no case were the crystals altered in form or angles, beyond the 

 tendency, shown in some of the solutions, for twins to form; or for the 

 relative sizes of the planes, in crystals showing two forms, to vary in the 

 different mixtures. The retarding of crystallization may be effected by 

 the addition of a 50 per cent solution of egg-white that has been treated 

 with ether and centrifugalized; the clear solution being used instead of 

 the blood plasma, and this is perhaps safer than the use of any saline solu- 

 tion. The addition of the plasma of the bloods of other species appears to 

 alter the angles slightly in some cases. All of the specimens examined 

 were oxyhemoglobin. 



