xlviii 



to exist between them. In the case of the paratartrate (racemate), 

 the liquid, originally inactive, exhibited, as the fermentation pro- 

 ceeded, a gradually stronger and stronger deviation of the plane of 

 polarisation to the left until the maximum was reached and the 

 fermentation ceased. It was then found that during the process of 

 fermentation the right-handed acid had been consumed, leaving the 

 left-handed acid alone master of the field ; and thus, freed from the 

 constraining influence of its right-handed brother, was able to assert 

 itself and exhibit, for the first time, its left-handed rotatory power. 

 Thus whilst right-banded and left-handed tartaric acids are chemi- 

 cally identical, and are distinguishable only by their crystalline form 

 and opposite action on polarised light, they are, nevertheless, utterly 

 different from a physiological point of view ; for the right-handed 

 tartaric acid is alone taken up and transformed by the fermentative 

 bacteria which refuse to have anything to do with the left-handed 

 tartaric acid. Thus the apparently trivial difference in the arrange- 

 ment of the atoms in space in the case of these two tartaric acids 

 makes an overwhelming difference in their physiological character. 

 A couple of years later, in 1856, the Royal Society conferred the 

 Rumford Medal on Pasteur " for his discovery of the nature of race- 

 mic acid and its relations to polarised light." 



A new chapter in Pasteur's life opens with the year 1854, when, at 

 the age of 32, he was nominated the first Dean of the Faculty of 

 Sciences which had just been created at Lille. In this capacity, at 

 once realising that the work of his department should, to some 

 extent, be brought into touch with one of the leading industries of 

 the district — the manufacture of alcohol from beetroot and grain — he 

 offered courses of lectures on fermentation, and with his character- 

 istic energy threw himself into the serious study of his subject. 



It is impossible here to pass even in the briefest review the history 

 of the progress made in the knowledge of fermentation before the 

 subject was attacked by Pasteur; suffice it to say that at this time 

 fermentation processes were not generally regarded as vital pheno- 

 mena at all. The dominant opinion concerning them was that enun- 

 ciated by Liebig, who viewed the classical transformation of sugar 

 into alcohol as a purely chemical process, depending not on the living 

 yeast cells which the microscope had revealed, but on the dead yeast 

 undergoing post-mortem decomposition : 



" Beer yeast, and in general all animal and vegetable matters in 

 putrefaction, impart to other bodies the state of decomposition in 

 which they are themselves. The movement, which by the disturbed 

 equilibrium is impressed on their own elements, is communicated 

 also to the elements of bodies in contact with them." 



Pasteur had been indirectly brought in contact with fermentation 

 phenomena in the course of his researches on asymmetry, for amongst 



