rod Munchhausen fashion, but as forming curls, according to the natural set of affinities"; and that "protoplasm, in fact, may be pictured as made up of a large number of curls, like a judge's wig—all in intercommunication through some center, connected here and there, perhaps, by lateral bonds of union." Ehrlich's conception of the molecule of functionally active protoplasm as consisting of a fundamental nucleus plus a large number of different chemical receptors or side chains is obviously at one with this stereochemical picture and he began to apply it as far back as 1885, in his studies on the oxygen requirements of the organism. In this important work he makes it clear that what he terms "color-analytics" (farbenanalytische Studien) is the most accessible way of investigating the intimate mechanism of intracellular or protoplasmic chemistry. He was early impressed (or as he himself puts it "obsessed") with the idea of a selective and distributive relation between definite chemical substances and definite body-tissues of the kind which chemists are agreed to describe as special "affinity." Starting with Hoppe-Seyler's observation that the emission and absorption of light in chlorophyll is accomplished, not by the entire chlorophyll molecule, but by certain specialized groups of atoms in it, he proceeds to outline the germinal idea of his side-chain theory, viz., that in the living cell the peripheral nutritive and excretory processes are accomplished by specialized atom groups of the protoplasmic molecule—the chemoreceptors. Suppose some extraneous substance, e. g., a food, a drug, or a poison, to be brought in juxtaposition with these peripheral receptive side-chains. Expressed in terms of thermodynamic chemistry we have the familiar Gibbsian problem in chemical equilibrium which Roozeboom has so picturesquely described as "the sociology of chemical substances." If the chemical and thermal relation of the substances is such that they will immediately and definitely combine, we shall have chemical and thermodynamic equilibrium; but if the effect of the external substance is stimulative or catalytic, the living protoplasm, having greater chemical energy and higher chemical potentiality, will expel a certain portion of itself to combine with the latter. Expressed in terms of stereochemistry, equilibrium is accomplished by the chemical
- "Das Sauerstoff-Bedürfniss des Organismus: Eine farbenanalytische Studie," Berlin, p. 885.
- It is interesting to note that the quasi-sexual concept of "chemical affinity" was first employed in science by a physician, Hermann Boerhaave ("Elementa chemise," Lugd. Bat., 1732, 677). Boerhaave says that when aqua regia dissolves gold the relation of the solvent to the solute is such that "each loves, unites with and holds the other"(amat, unit, retinet). The expression gained currency through its employment by Geoffrey and other French chemists to displace the old Newtonian concept of "attraction." (See Whewell's "History of Scientific Ideas," London, 1858. II., 15-20.) When Wagner's "Tristan und Isolde "was first produced, the symbolism of the philtre in the opera was chaffed by the humorists of the day as an instance of "chemische Liebe."