1907.] oil Dexterity and the Bend Sinister. 651 



nature. He himself said to a friend at that time : " I have made a 

 great discovery and am so elated that a nervous tremulousness has 

 seized me." And that great discovery was that the rotation of the 

 plane of polarisation of a ray of polarised light may be dextro-rotary 

 or lagvo-rotary according to the nature of the substance through which 

 it passes. The effect is as if the ray had been forced through a twisted 

 medium — a medium with a right-handed or left-handed twist, and 

 had itself received a twist in the process. Some substances produce 

 rotation only when in the crystallised state, but others are optically 

 active in solution. In the former case the molecules of the substance 

 have obviously no twisted structure, but they unite to form crystals 

 having such a structure. As Pasteur expressed it, we may build up 

 a spii'al staircase, an asymmetric figure from symmetric bricks ; when 

 the staircase is again resolved into its component bricks the asymmetry 

 ceases. It is the building and the builder that have done it. Dis- 

 cussing the question of the molecular constitution of dextro- and l^vo- 

 tartaric acid, he says : " We know on the one hand that the molecular 

 structures of the two tartaric acids are asymmetric, and on the other 

 hand that they are rigorously the same with the sole difference of 

 showing asymmetry in opposite senses. Are the atoms of the right 

 acid grouped in the spirals of a right-handed helm, or placed at the 

 soM angles of an irregular tetrahedron, or disposed according to some 

 particular asymmetric grouping or other ? We cannot answer these 

 questions, but it cannot be doubted that there exists an arrangement 

 of the atoms in asymmetric order having a non-superposable image. 

 It is no less certain that the atoms of the left acid realise precisely the 

 asymmetric grouping which is the inverse of this." 



It is not for me to discuss the question on which chemists have 

 been divided, whether Pasteur was right in regarding the formation 

 of asymmetric organic compounds as the special and exclusive pre- 

 rogative of the living organism. My point is to accentuate the all- 

 pervading character of asymmetrical arrangements throughout organic 

 nature. In the artificial production of unsymmetrical bodies it is 

 found that the two kinds, dextral and sinistral, are produced in equal 

 numbers, just as a glove-maker turns out an equal number of right 

 and left handed gloves, and by suitable means the two kinds can be 

 separated from each other. In nature, on the other hand, we find 

 that where, we have asymmetry the one kind of structure always 

 predominates over the other. The chemist in his laboratory produces 

 dextral and sinistral tartaric acid in equal quantities, but the grape 

 produces only dextral tartaric acid. Similarly the sugar-cane and 

 beetroot produce only dextral sugar, though as far as we know, it would 

 be equally easy for them to produce the sinistral, or a mixture of 

 both. It is not strange that there should be asymmetry in nature, 

 but it is strange that asymmetry should practically exist in one form 

 to the exclusion of the other, and that this should occur alike in 

 molecules and in plants and animals. Look at the human body. 



