214 THE POPULAR SCIENCE MONTHLY 



rod Munchhausen fashion, but as forming curls, according to the nat- 

 ural set of aflfinities " ; 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 mole- 

 cule 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 ac- 

 cessible 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 ab- 

 sorption 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 mole- 

 cule — the chemoreceptors. Suppose some extraneous substance, e. g., a 

 food, a drug, or a poison, to be brought in juxtaposition with these pe- 

 ripheral receptive side-chains. Expressed in terms of thermodynamic 

 chemistry we have the familiar Gibbsian problem in chemical equilib- 

 rium 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 SauerstofT-BedUrfniss des Organisraus : 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 " His- 

 tory of Scientific Ideas," Ix)ndon, 1858. II., 15-20.) When Wagner's "TrisUn 

 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." 



