CRYSTALLIZATION 313 



without leading to decided differences in the chemical behavior 

 of the haemoglobins which have not been observed by any in- 

 vestigator. Further doubt is thrown upon this interpretation 

 of the facts observed by Reichert and Brown by the observation 

 of Hiifner, recently confirmed with the utmost precision by 

 Butterfield (13), Heubner and Rosenberg (38), and Schumm (96) 

 that the characteristic absorption bands and the ratio of the 

 absorption of light in different parts of the spectrum of haemo- 

 globin is absolutely identical in species so far removed from one 

 another as the horse and man (Schumm) or the rabbit, sheep 

 and hog (Heubner and Rosenberg). Now these are properties 

 which we should anticipate might be materially affected by 

 internal differences of atomic arrangement. 



Further reason for doubting the correctness of referring the 

 differences of crystal structure displayed by the haemoglobins of 

 different animals to internal differences in the molecules of the 

 haemoglobins is supplied by the observation of Loeb and Brown 

 (54) that the crystal-form of the hcemoglobin of the mule is inter- 

 mediate in character between that of the horse and that of the donkey. 

 For if we assume that each different crystal form represents a 

 different internal atomic arrangement of the haemoglobin molecule, 

 then the number of such arrangements, even if very great, must 

 nevertheless be limited. The number of possible forms of crystals 

 must therefore also be limited and moreover the possible modi- 

 fications of forms must be discontinuous, i.e., there must exist 

 forms between which no intermediate forms are possible. This 

 being the case it would be very remarkable indeed were the hybrid- 

 ization of two closely related species to lead to the synthesis 

 of a new isomeric variety of haemoglobin not yet appropriated 

 by any existing species of animal and in addition lying between 

 the haemoglobins of the parent species. If analogous phenomena 

 should be displayed by all hybrids and by all varieties and mu- 

 tations that might have arisen or might conceivably arise in the 

 future we would have to admit that the haemoglobins already 

 recognizable as differing from one another in crystal form are 

 only a small proportion of those which are realizable. 



A much more reasonable supposition is that embodied in the 

 view that the differences in crystal form observed by Reichert 

 and Brown are attributable, not to the internal variation of atomic 

 grouping in the haemoglobin molecules but to external varia- 



