Excerpt from The Differentiation and Specificity of Corresponding Proteins and Other Vital Substances in Relation to Biological Classification and Organic Evolution: The Crystallography of Hemoglobins

Even the processes for preparing protein crystals are, except those of the hemoglobins, very limited in their range of usefulness, as has been shown by the failure to obtain crystals of even corresponding proteins save in a very limited number of instances. Moreover, the processes are so far from perfect that crystalline condition per se is not a guarantee that we have necessarily either a pure or a normal body; nor are such crystals free albumin, free globulin, etc., but acetates or sulphates or other forms of combination, etc. Moreover, when purification of proteins has been sought by repeated recrystallization it is by no means clear that the proc esses have not given rise to abnormal substances through a stripping off of very unstable or feebly combined radicals which constitute normal com ponents of the molecules, and which of course must contribute to giving the substance its peculiar properties. In the case of the hemoglobins it has been shown that decomposition products are formed at each step of recrystallization. It has even been found that crystalline habit may be so affected by recrystallization that a hemoglobin which normally appears in the form of hexagons may crystallize only in rhombic needles and tetra hedra.

We are not, however, without certain data which indicate differences of corresponding proteins. The very fact of the breaking down of the serum albumin and the serum globulin of the food during the processes of digestion, when these substances are in a natural state, can not be due to a non-absorbability, because in such form they may be rapidly absorbed under appropriate conditions, and it is at least suggestive that the degrar dation of the protein molecules must be, in part at least, for some important purpose in relation to the synthesis of the proteins of the individual. To what extent this disintegration is carried out we do not know, but from our present knowledge it is probable that the molecules are broken down into essentially the primary dissociation products. In what ways and from what derivatives the proteins of the individual are built up is a matter of speculation, but it seems at least that such analyses and syntheses mean a differentiation of the proteins of the food and the corresponding proteins of the animal.

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