138 CRYSTALLOGRAPHY OF HEMOGLOBIN IN RELATION 



metoxyhemoglobin has given rise to much confusion. It is clear that dif- 

 ferent observers of blood crystals have examined crystals of oxyhemoglo- 

 bin, reduced hemoglobin, metoxyhemoglobin, and methemoglobin in many 

 instances without making any distinction between them. Since these sub- 

 stances in a given blood may form quite different crystals, a source of the 

 variations in the recorded crystals of a given species is obvious. 



As has been shown, equally expert observers working with bloods of 

 the same species have arrived at very different conclusions as to the specifi- 

 city or non-specificity of hemoglobin crystals in relation to species, some 

 claiming that the crystals are occasionally specific, others that they are 

 always specific, and others that they are not specific because the same 

 blood may yield crystals of very different forms and that the differences 

 are probably accidental. Crystals of various colors and varying forms have 

 been obtained from the same blood. It has been held in favor of specificity 

 that recrystallization, even when frequently repeated, does not effect any 

 change in form; but this has been contradicted by observers who point to 

 final evidence to the contrary. How are these diverse conclusions to be 

 reconciled? 



In the first place, it is evident that the substance under investigation 

 was not always the same: sometimes it was oxyhemoglobin, or reduced 

 hemoglobin, or metoxyhemoglobin, or methemoglobin, etc. Any one of 

 these substances may appear in several forms of crystallization in the same 

 blood, often as many as three of them in the blood of a given species; and 

 it is even probable that there are other forms of hemoglobins present which 

 have not yet been isolated. But much more important even than these 

 sources of variation in the crystals was the failure of the observer to in- 

 terpret correctly his observations. The same crystal viewed in different 

 aspects presents different appearances, and the same crystal combination 

 may exist in different shapes due to the variation in crystal habit. The 

 expert microscopist might learn to interpret the different aspects presented 

 by a single crystal, but no one who is not a crystallographer would be 

 likely to suspect that a long rod-like crystal and a thin tabular crystal might 

 be the same combination of crystal forms. It was such failure to interpret 

 the forms observed that has caused the confusion between the apparent 

 octahedrons and the apparent 6-sided plates of the guinea-pig oxyhemo- 

 globin crystals that have been mentioned. An octahedron lying on one of 

 its faces and observed normal to this face has a hexagonal outline, and if it 

 grows lying on this face it will develop into a 6-sided (or a 3-sided) plate, 

 because it grows twice as fast parallel to the plane on which it lies as it does 

 normal to that plane, since it can not grow at all on the bottom plane. A 

 tabular crystal seen on edge looks like a rod or prism, and has been so 

 described by many observers. 



Actual errors in observation are very common. For instance, Bojan- 

 owski, owing to the nearly square prisms of the cat hemoglobin when seen 

 on edge, looks upon them as being 3-sidod prisms; and Friboes falls into 

 the same error, and even shows photomicrographs of the nearly square 

 orthorhombic prisms of the same substance, and refers to them as "3-sided." 



