314 PHYSICAL PROPERTIES 



tions in the milieu from which they are crystallized. The tech- 

 nique adopted by Reichert and Brown was to induce crystal- 

 lization directly in the laked blood. Now we know from the 

 observations of the immunologists that the blood plasma from 

 any species of animal differs antigenically from that derived 

 from any other species (62) and, since all known antigens are 

 proteins, we infer that the proteins, or, more probably, the com- 

 pound protein complexes (Cf. Chap. VII) in blood plasmas 

 derived from different species are in certain definite respects 

 different from each other. The crystals of each species studied 

 by Reichert and Brown were therefore deposited from a different 

 medium and it is not improbable that the observed differences 

 in the crystals are attributable to these known differences in 

 the media in which they were formed. It is well known that 

 crystal-habit is modified by alterations of the medium from which 

 the crystals are deposited. That modifications of this origin so 

 great as to preclude inclusion of the crystals formed in different 

 media in the same isomorphous series have not hitherto been 

 observed in the domain of inorganic chemistry is not improbably 

 attributable to the simpler character of the conditions accom- 

 panying crystallization in inorganic or non-colloidal media. We 

 have seen that there are many reasons for supposing that proteins, 

 even in solution, are disposed in a certain reticular structure 

 and if, as the facts dwelt upon in Chap. VII would seem to in- 

 dicate, characteristic protein complexes, formed by the union 

 in differing proportions of a relatively small number of simpler 

 protein components, exist in each type of blood plasma we may 

 well suppose that the reticular structures of the solutions com- 

 prising these plasma would likewise differ from one another. 

 Having regard to the markedly cohesive properties of proteins, 

 crystallization within the meshes of such a reticulum might 

 very conceivably, through external strains imposed by points 

 of attachment to the reticulum, modify the effects of the internal 

 strains which find their expression in crystal form. 



This hypothesis finds decided support in the fact first observed 

 by Halliburton (39) (31) and confirmed by Reichert (81) that 

 the crystal form of oxyhaemoglobin derived from a given species 

 may be profoundly modified by admixture with the blood of 

 another species. The following are illustrative results obtained 

 by Halliburton, the " normal" form of rat haemoglobin crystals 



