INTRODUCTION. 3 



certain peculiarities of substances which experience determined to be owing to differences 

 in chemical constitution, or the manner of linkage of the molecular components, and hence 

 should be expressed by structural formula>. Still later it was recognized that even the 

 structural formuhf, which obviously indicate the relations of the atoms and groups of 

 the molecule to one another in only two dimensions of space, are insufficient, and that 

 a full conception of the causes underlying the differences in isomers rests in the recogni- 

 tion of the arrangements of the molecular components or units in the three dimensions 

 of space or, in other words, to be recorded by space formuM. 



Stereochemistry, therefore, treats of the physical and chemical properties of atoms 

 or structural units in space of three dimensions, the arrangement of the component units 

 of the molecule being expressed by the term configuration of the molecule. This branch 

 of chemistry seems to have had its inception in an article by Wollaston in 1808, in which 

 he states that in order to understand the mutual relations of atoms we must have a geo- 

 metrical conception of their arrangements in all dimensions of space. But like many a 

 gem, it lay by the wayside unnoticed. Many years later (1848) Gmelin wrote that no 

 controversies as to the mode of writing formulae could be settled without the support 

 of a recognized conception of the arrangements of the atoms of the molecule. After another 

 such long period (1872), Wislicenus forcefully pointed out the insufficiency of structural 

 fornuite, and suggested that the deficiencies in our conceptions of the relations of atoms 

 could be accounted for in "the different positions of atoms in space." 



About a decade previous to this (1861), Pasteur made the first substantial step in 

 laying the foundation of stereochemistry by his investigations with tartaric acids, in which 

 he found that under proper conditions there could be obtained three kinds of tartaric 

 acid differing in crystalline form, and in optical, chemical, and physiological properties. 

 Two forms of these crystals he determined to be enantiomorphous, that is, related to one 

 another as an object is to its mirror-image, the hemihedral faces which appear on the 

 right side of one of the forms appearing on the left side of the other. Crystals that were 

 composed of equal quantities of these substances showed an absence of hemihedrism. 

 When the enantiomorphous forms were examined in polarized light it was found that 

 they were oppositely but equally optically active, one form rotating the ray of polarized 

 light to the right (dextro-rotatory), and the other to the left (tevo-rotatory) ; and that 

 when they were present in equal quantity the acid was inactive (racemic). Wlien solu- 

 tions of ordinary tartaric acid (dextro-tartaric acid) and of racemic tartaric acid (in the 

 form of tartrates, with a little albumin), were subjected to the influence of PenicilKum 

 glaucum, it was found, upon testing with the polarimeter, that as fermentation proceeded, 

 in the first solution optical activity decreased, and that the second or optically inactive 

 solution became active, but herein the plane of polarization was rotated to the left, or in 

 the opposite direction, and hence was tevo-rotatory. As fermentation progressed, optical 

 activity was correspondingly increased, and reached its highest limit when fermentation 

 ceased. Hence, in the racemic solution the acid was split, the dextro-tartaric acid being 

 consumed by the Penicillium as in the first solution, leaving the laivo-acid. All three 

 acids are in chemical composition and structural formula identical, yet, as will be observed, 

 they differ markedly, not only in their crystalline forms and optical properties, but also 

 to an extraordinary degree in their physiological peculiarities. Tins latter phenomenon, 

 as will be pointed out, is in its applications one of the most important in the whole domain 

 of protoplasmic processes. 



The principles underlying the work of Pasteur were developed in 1874 by van't Hoff 

 and Le Bel, working independently, who found that every optically active carbon com- 

 pound contained at least one asymmetric carbon atom, that is, an atom which has attached 

 to it four dissimilar elements, groups, or masses; and, moreover, that in order to explain 

 why this asymmetry should cause crystalline and optical asymmetry and the accompany- 



