192 



CRYSTALLOGRAPHY OF HEMOGLOBINS OF THE UNGULATES. 



1 : 10, or even flatter in very large rhombic plates; rarely in prismatic development 

 with the above ratio 2:1. The crystals are normally twinned "horse-type twin" (text 

 figures 110 and 111), with the two parts united along a prism-base edge and the axis of the 

 hemitrope twin normal to this common edge and in the basal pinacoid, which is the 

 ordinary composition plane. In some cases this composition plane is the plane normal 

 to the base, that includes the common edge, or is the so-called plane of twinning, normal 

 to the twin axis. In some crystals both of these composition planes occur in the same 

 individual, by one crystal overgrowing the other, over the common edge; and the two 

 uniting by filling up the re-entrant angle and forming the false plane normal to the base 

 and in the zone of the prism-base. In some cases the two parts of the twin are normally 

 developed crystals; but usually, when the base is the composition face, the two crystals 

 become elongated in the direction of the common edge (text figure 110), and the ratio 

 of length to breadth of such a crystal may be 6 : 1. Such crystals show the overlapping 

 at each end and recall the arrangement of the Carlsbad twin. When the composition 

 face is the twin plane, normal to the base, the two crystals may slightly overlap, or this 

 may not be noticeable and they are simply juxtaposed along this plane, recalling the 



a 



112 



FIGS. 108, 109, 110, 111, 112, 113. Equut caballut 0-Oxyhemoglobin. 



common gypsum twin on the orthopinacoid; and even becoming elongated along the 

 common edge, but not to the same extent as in the case when the base is the composition 

 face. Another hemitrope twin of this type is possible in which the twin axis is the com- 

 mon prism-base edge and the composition face is the base or the normal to the base. 

 This also appears to occur, but not so commonly. There is a third kind of twinning that 

 was occasionally seen, of the Manebach type (text figure 112), when the base is the com- 

 position face and twinning plane, or the normal to the base is the twin axis. From the 

 way in which these twins develop it would seem better to assume a twin axis parallel 

 to the edge 010-001, and then the twinning; plane would be the plane normal to the base 

 in the zone of (lOO)-(OOl). This plane actually appears to occur as a composition face 

 in these twins. In the first type of twinning (horse-type) especially, when the base is 

 the composition plane, they twin several times on the different prism edges so that three 

 or more may occur in a group (text figure 113), in partial polysynthetic order. In some 

 cases this produces a six-pointed star with three individuals, or more often with four. 



These monoclinic crystals are produced in great numbers in the blood to which 

 oxalate has been added, and they increase in proportion to the amount of oxalate added, 

 and also in inverse proportion to the number of a-oxyhemoglobin crystals. But they 

 are produced in blood to which no oxalate has been added, although in comparatively 

 small numbers. The oxalate does not alter the habit, form, or other characteristics of 

 the crystals at all. They form evidently from concentrated or dense solutions of the 

 hemoglobin, and the function of the oxalate is perhaps to increase the pressure of the 

 solution or to make it more concentrated by taking some of the water. Slow evaporation 

 of non-oxalated blood has the same effect of making the solution more dense. It is also 

 possible that the oxalate helps to convert one isomer into another. 



