102 INVESTIGATIONS OF PREYER 



axis does not lie parallel to the direction of the polarized light ray. Preyer 

 goes on to state that if future investigations should show that all blood 

 crystals are either rhombic or hexagonal, which is probably true, then it 

 could not be maintained that the difference in the forms of the crystals 

 is a case of polymorphism or dimorphism, because chemical identity is 

 lacking. 



The hexagonal system, as A. Schrauf (Jahrbuch f. Mineralogie, 1865, 

 46) has_shown, is conceived of as being a peculiar combination of the rhom- 

 bic (P.P oo , with the single condition that oo P: oo P= 60), therefore the mis- 

 take could be made of looking upon the crystallographic distinction as being 

 a material one. The statement of Schrauf does not, however, bear the test, 

 because even if the hexagonal forms are still the simple combination of the 

 rhombic, the fundamental optical distinction of both systems can not be 

 denied. Optically the rhombic crystals are biaxial and the hexagonal are 

 uniaxial. 



There exist other distinctions outside of the crystallographic systems. 

 The peculiar crystalline form in relation to each kind of animal (of the 

 guinea-pig, the sphenoidal; of the dog, 4-sided prisms; of man, these and 

 rhombic plates, and so forth) is so constant and definite that only these 

 forms could be obtained from the blood referred to. After recrystallization 

 repeated ever so often the same form always appears, which is peculiar to 

 each kind of animal, and which can not be changed to another (see Chapter 

 VII). The same applies to solutions of hemoglobin. Yet little importance 

 is to be attached to statements on the crystallographic differences of the 

 hemoglobin of different animals, because neither is the same method of 

 crystallization always used, nor is the blood always capable of being com- 

 pared, nor has a measure of the crystallizability of any optional substance 

 been found. 



It is the same with decomposability as with the crystallizability of 

 hemoglobin. Both vary according to the species of animal, but the investi- 

 gations undertaken in this direction suffer from so many and such large 

 errors that they prove nothing beyond what has long been known the 

 different quantitative determinations of the blood-coloring matter in 

 various animals and individuals. Such matters lead to the desire to follow 

 up through a series of animals the several properties of hemoglobin for 

 example, the coagulation-point, the crystalline form, and the capacity of 

 water of crystallization in order that the question concerning their great 

 differences might be more closely approached : whether the various hemo- 

 globins are present as so many different substances which only agree in cer- 

 tain characteristics, or whether they are entirely identical in derivation and 

 their differences come about solely because of combining with other sub- 

 stances, or are properties of the crystals. Perhaps an explanation could be 

 obtained by transfusion, as, for example, of squirrel's blood to guinea-pig, or 

 vice -versa. 



The following table (table 31) is from Preyer, and is an excellent sum- 

 mary of our knowledge of the crystallography of hemoglobin up to the tune 

 of the publication of his memoir. 



