530 Professor Percy F. FranJcland [Feb. 19, 



During the past few years no chemical researches have com- 

 manded more interest, both on account of their theoretic importance 

 and the fertility of resource exhibited in their execution, than those of 

 Emil Fischer's, which have led to the artificial preparation in the 

 laboratory of several of the various forms of sugar occurring in nature, 

 as well as of other sugars not hitherto discovered amongst the pro- 

 ducts of the animal or vegetable kingdoms. The natural sugars are 

 all of them bodies with dissymmetric molecules, powerfully affecting 

 the beam of polarised light, but when prepared artificially they are 

 without action on polarised light because in the artificial product 

 the left-handed and right-handed molecules are present in equal 

 numbers, the molecules of the one neutralising the molecules of the 

 other and thus giving rise to a mixture which does not affect the 

 polarised beam either way. By the action of micro-organisms, how- 

 ever, on such an inactive mixture, the one set of molecules is searched 

 out by the microbes and decomposed, leaving the other set of mole- 

 cules untouched, and the latter now exhibit their specific action on 

 polarised light, an active sugar being thus obtained. 



The most suitable micro-organisms to let loose, so to speak, on 

 such an inactive mixture of sugar-molecules, are those of brewers' 

 yeast, which decomj)ose the sugar molecules with formation of 

 alcohol and carbonic anhydi'ide. Their action on these inactive 

 artificial sugars of Fischer's is particularly noteworthy. 



One of the principal artificial sugars prepared by Fischer is 

 called fructose, it is inactive, but consists of an equal number of 

 molecules of oppositely active sugars called Isevulose. 



One set of these leevulose-molecules turns the plane of polarisa- 

 tion to the right, and we may call them right-handed Isevulose^ whilst 

 the other set of Isevidose-molecules turns the plane of polarisation to 

 the left, and we may call them left-handed Isevidose. 



The left-handed laBvulose occurs in nature, whilst the right- 

 handed l^vulose, as far as we know, does not. Now, on putting 

 brewers' yeast into a solution of the fructose, the yeast-organisms 

 attack the left-handed laevulose molecules and convert them into 

 alcohol and carbonic anhydride, whilst the right-handed laevulose is 

 left undisturbed. The yeast organisms thus attack that particular 

 form of laevulose of which their ancestors can have had experience 

 in the past, whilst they leave untouched the right-handed laevulose 

 molecules, w^hich being a new creation of the laboratory, they have 

 no hereditary instinct or capacity to deal with. 



This selective power is possessed also by other forms of micro- 

 organisms besides the yeasts, which are indeed only suitable for 

 the separatory decomposition of sugars, and by means of bacterial 

 forms a much greater variety of substances can be attacked in this 

 manner. Thus I have recently found that glyceric acid can be 

 decomposed by the B. ethaceticus, to which I have already referred 

 this evening. 



