360 VEHICLES OF CHEMICAL CORRELATION 



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 differ- 

 ences between 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 prevent 

 inclusion of the crystals formed in different media in the same iso- 

 morphic series, have not hitherto been observed in the domain of inor- 

 ganic chemistry is not improbably attributable to the simpler character 

 of the conditions accompanying crystallization in inorganic or non- 

 colloidal media. We have seen that there are many reasons for sup- 

 posing that proteins, even in solution, are disposed in a certain reticular 

 structure (cf. Chapter XIII), and if, as the facts which we dwelt upon 

 in connection with the properties of the compounds of proteins with 

 each other would seem to indicate, 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 structure of the solu- 

 tions comprising these plasma would likewise differ from one another. 

 Having regard to the markedly cohesive properties of proteins, crystal- 

 lization within the meshes of such a reticulum might very conceivably, 

 through external strains imposed by points of attachment to the reticu- 

 lum, modify the effects of the internal strains which find their expres- 

 sion in crystal form. 



This hypothesis finds decided support in the fact, first observed 

 by Halliburton, and confirmed by Reichert, that the crystal form of 

 oxyhemoglobin derived from a given species may be profoundly 

 modified by admixture with the blood of another species. The follow- 

 ing are illustrative results obtained by Halliburton, the "normal" 

 form of rat-hemoglobin crystals being rhombic, those obtained from 

 guinea-pigs being normally tetragonal, and those from squirrels' blood 

 hexagonal. 



Form of hemoglobin crystals deposited 

 Blood of Mixed with that of from the mixture. 



Rat Squirrel Both rhombic prisms and hexagons present. 



Rat Guinea-pig No rhombic prisms of the shape usually seen 



in rats' blood present; no tetrahedra; 

 crystals are all rhombic prisms with 

 hexagonal habit. 



Squirrel Guinea-pig Hexagonal plates and retrahedra both 



present; many tetrahedta imperfect; the 

 tetrahedra all reduced to about half the 

 si2e of those prepared from the unmixed 

 blood of the same guinea-pigs. 

 Squirrel Fine rhombic needles and hexagonal plates 



both present in abundance. 



Guinea-pig The greater number of the crystals formed 



are very small tetrahedra about a quarter 

 the size of those prepared from the blood 

 of the same guinea-pig. The optical 

 properties are, however, the same; rhom- 

 bic prisms, very slender, like those of 

 dogs' blood are also seen. 



