Crystallography of Hemoglobins. 



67 



crystals from the different genera. When the characters of the 

 crystals from any one of these genera are tabulated, they at once 

 recall to the mineralogist the crystallographic groups of minerals. 

 The crystals of the genus Felis are as strictly isomorphous as those 

 of the calcite group of the rhombohedral carbonates. As an ex- 

 ample of the individuality of these generic characters, the following 

 example may be cited : A sample of blood, marked as that of 

 a certain species of baboon was received from one of our zoologi- 

 cal gardens. Upon making preparations and examining the crys- 

 tals, it was at once evident that they did not correspond to any 

 species of baboon thus far examined, nor did they show the char- 

 acters of the crystals of this genus. They were identified by their 

 crystallographic characters as belonging to the cats (genus Felis), 

 but not to any species thus far examined. Inquiry at the zoological 

 garden from which the blood was received showed that the animal 

 recorded as being subjected to a postmortem examination on the 

 date when the blood was collected was a species of cat (genus Felis), 

 but not one of which we had previously examined the blood. 



2. Specificity in the crystals of a genus. — The crystals of dif- 

 ferent species of a genus can usually be distinguished from each 

 other by definite differences of angle, when they are favorable for 

 good measurement, while preserving their isomorphous character 

 as belonging to a definite genus. From the difficulty of measure- 

 ment in many cases it is hard to give these differences a quantita- 

 tive value, but the variation in habit of the crystals and their mode 

 of growth will often show specific differences. 



3. The occurrence of several types of crystals of oxyhemoglobin 

 in many species. — The oxyhemoglobin of some of them is di- 

 morphous, crystallizing in two systems, or even trimorphous in 

 many cases. Here it is generally seen that the crystals first formed 

 crystallize in a system of a lower grade of symmetry than those 

 formed later. When several types of crystals occur in the species 

 of a genus, they may each be arranged in isomorphous series. The 

 explanation of these observations seems to be indicated by the 

 results obtained. 



4. The constant recurrence of certain angles, either plane or di- 

 hedral, in oxyhemoglobin, hemoglobin, and the " methemoglobin " of 

 various species, eve?i when widely separated zoologically and when 



