TO SPECIES, ACCORDING TO PREVIOUS INVESTIGATORS. 137 



partly colorless." This is a description of the method of producing crystals 

 of metoxyhemoglobin, and the colors described are such as would be found 

 in metoxyhemoglobin crystals that were rather insoluble, as these are 

 described as being. He made a similar observation upon the crystals from 

 the cat. 



Weir Mitchell describes the production of crystals of oxyhemoglobin 

 from the blood of the sturgeon, and states that their color may be com- 

 pletely removed by alcohol and water without injury to the form, and that 

 these decolorized crystals may be dissolved in water and recrystallized in 

 the original form. 



Struve (Ber. d. d. chem. Ges., 1881, xiv, 930) decolorized blood crystals 

 by treating them with dilute alcohol, but without causing any change of 

 form. In a later communication (Jour. f. prakt. Chem., N. F., 1884, xxix, 

 304) he gives a more detailed description of his observations: Fresh blood 

 crystals placed in an excess of alcohol change their color to a darker tint, 

 without change of form, and become insoluble in water and alcohol. This, 

 he states, is due to a loss of water of crystallization and going over into an 

 amorphous condition. These altered crystals by treatment with ammoniacal 

 alcohol, by glacial acetic acid, or by concentrated sulphuric acid are decol- 

 orized without change of form. Struve did not dissolve and recrystallize 

 them. The color extracted he regards as a hematin derivative, which he 

 names hematin acid. His conclusion is that hemoglobin crystals are a col- 

 orless albuminous substance, mechanically mixed with a coloring matter. 



On reading the descriptions of Struve it seems evident that the treat- 

 ment with alcohol changes the crystals of hemoglobin by hardening them, 

 an effect of alcohol upon albuminous substances generally ; and if he started 

 with oxyhemoglobin the darkened crystal treated with alcohol was already 

 a different substance, a pseudomorph in fact. Such a pseudornorph might 

 retain its form even though the substance of which it was composed should 

 be the original material decomposed. In inorganic substances we find for 

 instance crystals of pyrite, FeS 2 , changed by pseudomorphism into limonite, 

 Fe 4 3 (OH) 6 without the slightest change in outward form; fluorite, CaF 2 , 

 in this way is changed to quartz, Si0 2 . The colorless crystals obtained by 

 treatment of the alcoholized crystals with the agents mentioned above are 

 but skeletons of the original oxyhemoglobin crystals, and may have quite a 

 different composition. As Struve states, they are amorphous and not really 

 crystals at all. But Weir Mitchell's recrystallized colorless crystals are not of 

 this kind, and are not to be explained in the light of our present knowledge. 



Colorless blood crystals are (with the exception of the recrystallized 

 colorless forms described by Weir Mitchell) to be accounted for by a change 

 of oxyhemoglobin to metoxyhemoglobin, by pleochroism, or by pseudo- 

 morphism in case of chemically treated crystals. 



Besides colorless and slightly colored crystals, other variations from the 

 typically colored oxyhemoglobin crystals have been observed. Thus, we 

 find records of "bluish," "purple," and "pink" crystals that are evidently 

 reduced hemoglobin; and "yellowish" and "brownish" crystals that may 

 be methemoglobin. The failure to distinguish between methemoglobin and 



