CRYSTALLOGRAPHY OF THE HEMOGLOBINS OF AVES. 165 



Habit thin tabular in simple crystals (text figure 37), becoming thicker by homo- 

 geneous regular growth, in which the prism-base edge of one member of the group is in 

 line with prism-base edge of the next following layer (text figure 38); the successive 

 layers arranged in polysynthetic order (text figure 39). Composite crystals are produced 

 by this piling up of the successive individuals of the group, that finally develop angles 

 of 90 for the plate, by averaging of the angles 88 and 92; the result not being dis- 

 tinguishable from a tetragonal crystal when examined on the flat, and even giving a 

 dusky uniaxial cross in convergent light. This kind of crystal shows the composite 

 character by being less regularly developed than the simple crystal. On edge the sepa- 

 rate individuals in the group are at once distinguished by pleochroisni, using one nicol, 

 and with crossed nicols by the difference of double refraction. Some were seen consisting 

 of two or three individuals, but many consisted of a much larger number in the poly- 

 synthetic arrangement. The crystals were large, but did not grow into arborescent 

 groups as in the case of those from the blood of Olor buccinator. 



Pleochroism is rather marked on the flat view, less so on the edge; the absorption is 

 c > b > a. The colors are shades of the oxyhemoglobin red, a being yellowish-red. 

 The orientation of the elasticity axes is a=a, b=c, c=6; the optic axes being in the 

 plane of the basal pinacoid. No interference figure appears therefore on the flat view 

 (001) ; but on edge, when looking nearly along a, one brush of the figure is seen. In the 

 composite crystals this also is visible, the arrangement of their elasticities being as shown 

 in text figure 39. From these figures it is seen that the axis b keeps its position in the 

 regular growth, and the axes a and c alternate in the successive layers. In case of very 

 thin layers in the composite crystals, so that the layers become too thin to show by the 

 microscopic examination, this averaging of a and c would greatly reduce the amount 

 of the double refraction, so that it might become almost zero, which is the condition in 

 the species of swan examined, and leads to the suspicion that in the blood of Olor buc- 

 cinator the crystals are only pseudo-tetragonal. From the position of the brush of the 

 interference figure it is evident that the acute bisectrix Bx a =n, and the optical character 

 is negative. 



The mimetic crystals produced by the homogeneous regular growth are singly 

 refracting when examined on (001) and are not strongly doubly refracting when examined 

 on edge view, especially when the individual layers are thin and not of the same thick- 

 ness throughout; they are hence in some cases truly pseudo-tetragonal. The averaging 

 of the angles of 88 and 92 to 90 makes them strictly tetragonal in form. 



CHICKEN, Gallus domestica. Plate 11. 



Blood was obtained from the living chicken, oxalated and centrifu- 

 galized, and only the corpuscles used. The corpus- 

 cles were treated by the usual method and crystal- 

 lized at a temperature near the freezing-point. All 

 examinations had to be made at the same low tem- 

 perature, the room being kept at about the freezing- 

 point or below. Very few slides showed crystals, 

 and they were usually isolated or in small groups. 

 Blood from two different birds was examined at 

 different times, but the habit was about the same 

 in both cases. The crystals were oxyhemoglobin. 



Oxyhemoglobin of Gallus domestica. 



Orthorhombic : Axial ratio a : b : c =0.949 : 1 : c. 



Forms observed: Prism (110), base (001). 



Angles: 110 A 110=87 (normals); 110 A 001 =90. Flos ' 40 ' 4J 



