542 



SCIENCE. 



[N. S. Vol. XII. No. 303. 



This is an old story for us, but at that 

 time it appeared highly improbable, and 

 even Biot, the veteran discoverer of the 

 optical rotation of dissolved organic sub- 

 stances, who had for twenty years vainly 

 endeavored to convince chemists that in 

 the study of this phenomenon was to be 

 found one of the best means of investiga- 

 ting molecular structure, entertained strong 

 doubts as to its accuracy. As an illustra- 

 tion of scientific skepticism, I may quote 

 Pasteur's own words, relating to Blot's re- 

 ception of his discovery : * " He (Biot) 

 summoned me to bis laboratory, in order 

 to have me repeat the various experiments 

 under his own eyes. He supplied me with 

 racemic acid, which he himself had exam- 

 ined and had found to be optically inactive. 

 I prepared in his presence the sodium-am- 

 monium double salt, for which he wished 

 to furnish even the soda and ammonia. 

 The solution was set aside in his laboratory 

 to evaporate slowly, and after 30-40 grams 

 of crystals had formed, he again summoned 

 me to the College de France to collect the 

 dextro- and Isevo-rotatory crystals, and 

 separate them according to their crystallo- 

 graphic character, requiring me to repeat 

 the assertion that those which I placed 

 at his right hand were dextro-rotatory, 

 and those at his left hand Isevo-rotatory. 

 When this was done, he said that he him- 

 self would carry out the rest. He carefully 

 prepared the solutions and at the moment 

 when he was about to observe them in the 

 polarimeter he called me again into his 

 room. He first brought into the apparatus 

 the more interesting solution, that which 

 should rotate towards the left. Without 

 making the reading, merely by viewing the 

 shades of color on the two halves of the 

 field of vision, he recognized the presence 

 of distinct Isevo-rotation. Then the old 

 man, visibly affected, grasped my hand and 



*Ostwald's Klassiker, No. 28, p. 14. This con- 

 tains Pasteur's own account of his observations. 



said, ' my dear child, I have loved science 

 my whole life so much that I hear my heart 

 beating for joy.' " 



Pasteur was able to give but a vague, yet 

 true explanation of his observations. He 

 attributed this physical isomerism to a sort 

 of asymmetry of the molecule, the two kinds 

 being identical in every respect except that 

 they cannot be made to coincide ; they are 

 like an object and its reflection in a mirror, 

 the right and left hand, or a right- and left- 

 handed screw. In his opinion, the asym- 

 metry was caused by the action of forces 

 peculiar to the organism. 



Pasteur's discovery waited long before 

 exercising a perceptible influence on the 

 course of chemical research . Kekule's Lehr- 

 huch, published in 1866, describes the facts, 

 but makes no mention of Pasteur's theo- 

 retical views. The investigations of Wisli- 

 cenus, on the lactic acids, published in 1869, 

 showed that four of these exist (/3 oxypro- 

 pionic acid and two optically opposite forms 

 of a oxypropionic acid with their racemic 

 combination), while the structure theory 

 indicates but two. Without giving a more 

 concise explanation, be suggested that the 

 difference of the acids is a geometrical one, 

 and called this kind of isomerism geometrical 

 isomerism. It is curious that at even this 

 date Wislicenus makes no mention of Pas- 

 teur's discovery of the enantiomorphic 

 tartaric acids or his theory of molecular 

 asymmetry, although the facts were pre- 

 cisely analogous, and the explanation a 

 more definite one than his own. 



Pasteur's conception of molecular asym- 

 metry, first stated, I believe, in 1860, had 

 to wait until 1874 before assuming a form 

 sufiBciently definite to admit of application 

 to the theory of structure. In this year 

 there appeared independently and almost 

 simultaneously two publications of essen- 

 tially similar nature, the one by Le Bel in 

 Paris, the other by van't Hofi', then pro- 

 fessor in Utrecht. Le Bel acknowledged 



