June 9, 1892] 



NATURE 



139 



pushed, for although niannite and dulcite are extremely similar 

 substances, they are not chemically identical. We are 

 acquainted, however, with substances which, though chemically 

 identical, are different in respect of certain physical properties, 

 and are hence known as physical isomers. It is in explanation 

 of this physical isomerism that one of the most beautiful of 

 chemical theories was propounded by Lebel and Van 't Hoff in 

 1874, and which remains unsupplanted to the present day. 



This theory depends upon taking into consideration the dis- 

 symmetry of the molecule which is occasioned by the presence 

 in it of a carbon-atom which is combined with four different 

 atoms or groujis of atoms, and is most easily intelligible from an 

 inspection of iliese two models. [Demonstration of tetrahedral 

 models of asymmetric carbon-atom,] 



This molecular dissymmetry is specially exhibited in the 

 crystalline form of such substances, and in their action upon 

 polarized light. 



The molecule arranged according to the one pattern has the 

 property of turning the plane of polarization in one direction, 

 whilst the molecule arranged according to the other pattern has 

 invariably the property of tnrning the plane through precisely 

 the same angle in the opposite direction. The molecular dis- 

 symmetry ceases when two such molecules combine together, the 

 resulting molecule having no action on polarized light at all. 



The interest of these phenomena in connection with micro- 

 organisms lies in the fact that they are sometimes possessed of 

 the powtrr of discriminating between these physical isomers. 

 Althoiigli this remarkable property was demonstrated years ago 

 by Pasteur in respect of the tartaric acids, it has only compara- 

 tively rarely been taken advantage of. Recently, however, 

 hemical science has been enriched in several instances by suc- 

 jessfully directing the energies of microorganisms in such work 

 >f discrimination. 



Durmg the past few years no chemical researches have com- 

 manded more interest, both on account of their theoretic import- 

 ance and the fertility of resource exhibited in their execution, 

 ihan 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 products of the animal or vegetable 

 kingdoms. The natural sugars are all of them bodies with 

 dissymmetric molecules, powerfully affecting the beam of 

 polarized light, but when prepared artificially they are without 

 action on polarized light, because in the artificial product the 

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

 numbers, the molecules of the one neutralizing the molecules of 

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

 the polarized beam either way. By the action of micro- 

 organisms, however, on such an inactive mixture, the one set of 

 molecules is searched out by the microbes and decomposed, 

 leaving the other set of molecules untouched, and the latter now 

 exhibit their specific action on polarized 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 decompose the sugar molecules with for- 

 mation of alcohol and carbonic anhydride. Their action on 

 these inactive artificial sugars of Fischer's is particularly note- 

 worthy. 



One of the principal artificial sugars prepared by Fischer is 

 called/rwr/^ji?,- it is inactive, but consists of an equal number of 

 molecules of oppositely active sugars called Itzvtilose. 



One set of these laevulose- molecules turns the plane of polariza- 

 tion to the right, and we may call them right-handed hevtilose, 

 whilst the other set of Icevulose-molectdes turns the plane of 

 polarization to the left, and we may call them left-handed 

 i(CvuIose. 



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

 handed laevulose, 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, which, being anew 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 



NO. [ 1 80, VOL. 46] 



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. ethaccticus, to which 

 I have already referred this evening. 



This glyceric acid is thus represented by chemists : — 

 (CH.pH) 



C3H6O4 or (H)-C(OH) 



(COOH) 



and this should, according to Le Bel and Van 't Raff's theory, 

 be capable of existing in two physically isomeric forms, as 

 easily shown by our models. 



The ordinary glyceric acid known to chemists is, however, 

 quite inactive to polarized light, and must consist, therefore, of 

 a combination in equal molecules of a right-handed and left- 

 handed glyceric acid. Now whea the B. ethaceticus is put into 

 a suitable solution of the calcium salt of this glyceric acid, it 

 multiplies abundantly, and completely consumes the right-handed 

 molecules of the salt, but leaves the left-handed inolecules 

 entirely intact, a powerfully active glyceric acid being thus 

 obtained. [Demonstration of the laevorotary power of solution 

 ofnew zinc glycerate with projection-polariscope.] 



A number of derivatives of this new active glyceric acid have 

 recently been prepared in my laboratory — 



Derivatives of Active Glyceric Acid. 

 Formula. Specific Rotation. 



[«]« 

 (CsHsOgX^Ba -f- 2H2O - 9° 



(C3H503)oSr -t- 3H.,0 - lo 



(C3H503).,Ca + 2H.,0 - 12 



(C3H503).,Cd -f liHoO - 14 



(C3Hg03)2 Zn -f H,0 - 22 



(CaHgOa)^ Mg -t- H^O . - iS'S 



CsHflOsNa I - 16 



C3Hg0.j Am I - 20 



C3H5O3 K - 15 



C3H5O3 I i - 20-5 



CjHsOsMe - 4-8 



C3H5O3 Et - 9-2 



C3H5O3 Pr («) - 13-0 



Here again, then, chemistry has been enriched by a number of 

 new comjwunds, which we owe entirely to the unaccountable 

 cap: ice of this micro-organism. 



Individuality of Micro-organisms. 



Although micro-organisms are thus becoming more and more 

 indispensable reagents in the chemical laboratory, essential as 

 they are for the production of many bodies, it is always necessary 

 to bear in mind that by virtue of their vitality their nature is 

 infinitely more complex than that of any inanimate chemicals 

 which we are accustomed to employ. In a chemically pure 

 substance we believe that one molecule is just like another, and 

 hence we expect perfect uniformity of behaviour in the molecules 

 of such a pure substance under prescribed conditions. I n a pure 

 cultivation of a particular species of micro-organism, however, 

 we must not expect such rigid uniformity of behaviour from each 

 of the individual organisms making up .such a cultivation, for 

 there may be and frequently are great differences amongst them; 

 in fact, each member of such a pure culture is endowed with a 

 more or less marked individuality of its own, and these possible 

 variations have to be taken into consideration by those who wish 

 to turn their energies to account. In fact, experimenting with 

 micro-organisms partakes rather of the nature of legislating for 

 a community than of directing the inanimate energies of chemical 

 molecules. Thus frequently the past history of a group of micro- 

 organisms has to be taken into account in dealing with them, 

 for their tendencies may have become greatly modified by the 

 experiences of their ancestors. 



Of this I will give you an instance which has recently come 

 under my observation : — 



Here is a bacillus, which has the property of fermenting 

 calcium citrate ; I have found that it can go on exerting this 

 power for years. On submitting this fermenting liquid to plate- 

 cultivation, we obtain the appearances which you see here. 

 [Lantern-demonstration of plate-culture of bacillus which fer- 

 ments calcium citrate.] 



