September 8, 1898] 



NA TURE 



453 



molecular asymmetry in organic compound?. The extraordinary 

 subtlety of the nir)des of isomerism then for the first time dis- 

 closed ; the novelty and refinement of the means employed in 

 the separation of the isomerides ; the felicitous geometrical 

 hypothesis adopted to account for the facts — an hypothesis 

 which subsequent investigation has served but to confirm ; the 

 perfect balance of inductive and deductive method ; and lastly, 

 the circumstance that in these researches Pasteur laid the 

 foundation of the science of stereochemistry : these are charac- 

 teristics any one of which would have sufficed to render the 

 work eminently noteworthy, but which, taken together, stamp 

 it as the capital achievement of organic chemistry. 



Physiologists, on the other hand, are naturally more attracted 

 by Pasteur's subsequent work, in which the biological element 

 predominates : in fact, I doubt whether many of them have 

 given much attention to the earlier work. And yet it ought to 

 be of interest to physiologists, not merely because it is the root 

 from which the later work springs, but because it furnishes, I 

 am convinced, a reply to the most fundamental question that 

 physiology can propose to itself — namely, whether the phe- 

 nomena of life are wholly explicable in terms of chemistry and 

 physics ; in other words, whether they are reducible to pro- 

 blems of the kinetics of atoms, or whether, on the contrary, 

 there are certain residual phenomena, inexplicable by such 

 means, pointing to the existence of a directive force which 

 «nters upon the scene with life itself, and which, whilst in no 

 way violating the laws of the kinetics of atoms — whilst, indeed, 

 acting through these laws — determines the course of their 

 operation within the living organism. 



The latter view is known as Vitalism. At one time univers- 

 ally held, although in a cruder form than that just stated, it 

 fell, later on, into disrepute; "vital force," the hypothetical 

 and undefined cause of the special phenomena of life, was rele- 

 gated to the category of occult qualities ; and the problems of 

 physiology were declared to be solely problems of chemistry 

 and physics. Various causes contributed to this result. In the 

 first place, the mere name "vital force" explains nothing; 

 although, of course, one may make this admission without 

 thereby conceding that chemistry and physics explain every- 

 thing. Secondly, the older vitalists confounded force with 

 energy; their "vital force" was a source of energy; so that 

 their doctrines contradicted the law of the conservation of energy, 

 and became untenable the moment that this law was established. 

 I would point out, however, that the assumption of a purely 

 directive " vital force," such as I have just referred to, using 

 the word "force" in the sense which it bears in modern 

 dynamics, does not necessarily involve this contradiction ; for a 

 force acting on a moving body at right angles to its path does 

 no work, although it may continuously alter the direction in 

 which the body moves. When, therefore, Prof. J. Burdon 

 Sanderson writes : " The proof of the non-existence of a special 

 ' vital force ' lies in the demonstration of the adequacy of the 

 known sources of energy in the organism to account for the' 

 actual day by day expenditure of heat and work," he does not 

 consider this special case. The application of the foregoing 

 principle of dynamics to the discussion of problems like the 

 present is, I believe, due to the late Prof. Fleeming Jenkin. A 

 third ground for abandoning the doctrine of a " vital force" was 

 the discovery that numerous organic compounds for the produc- 

 tion of which the living organism was supposed to be necessary, 

 could be synthesised by laboratory methods from inorganic 

 materials. It is the validity of some of the conclusions drawn 

 from the latter fact that I wish especially to consider. 



Recent years have, however, witnessed a significant revival of 

 the doctrine of vitalism among the physiologists of the younger 

 generation. 



It is not my intention to offer any opinion on the various 

 arguments which physiologists of the neo-vitalistic school have 

 put forward in support of their views ; these arguments and the 

 tacts on which they are based lie entirely outside my province. 

 I shall confine myself to a single class of chemical facts rendered 

 accessible by Pasteur's researches on optically active compounds, 

 and, considering these facts in the light of our present views 

 regarding the constitution of organic compounds, I shall en- 

 deavour to show that living matter is constantly performing a 

 certain geometrical feat which dead matter, unless indeed it 

 hapi>ens to belong to a particular class of products of the living 

 organism and to be thus ultimately referable to living matter, is 

 incapable — not even conceivably capable — of performing. My 

 argument, being based on geometrical and dynamical considera- 



NO. 1506, VOL. 58] 



tions, will have the advantage, over the physiological arguments, 

 of immeasurably greater simplicity ; so that, at all events, any 

 fallacy into which I may unwittingly fall will be the more readily 

 detected. 



In order to make clear the bearing of the results of stereo- 

 chemical research on this physiological problem, it will be 

 necessary to give a brief sketch of the stereochemistry of optically 

 active organic compounds, as founded by Pasteur and as further 

 developed by later investigators. 



Substances are said to be optically active when they produce 

 rotation of the plane of polarisation of a ray of polarised light 

 which passes through them. The rotation may be either to the 

 right or to the left, according to the nature of the substance ; 

 in the former case the substance is said to be dextro-rotatory ; 

 in the latter, Ictvo-rotatory. The effect is as if the ray had been 

 forced through a twisted medium— a medium with a right- 

 handed or a left-handed twist — and had itself received a twist 

 in the process ; and the amount of the rotation will depend 

 upon the degree of " twist" in the medium (that is, on the 

 rotatory power of substance) and upon the thickness of the 

 stratum of substance through which the ray passes, just as the 

 angle through which a bullet turns in passing from the breech to 

 the muzzle of a rifle will depend upon the degree of twist in the 

 rifling and the length of the barrel. If the bullet had passed 

 through the barrel in the opposite direction, the rotation would 

 still have been in the same sense ; since a right-handed (or left- 

 handed) twist or helix remains the same from whichever end it 

 is viewed, in whichever direction it is traversed. This also 

 applies to optically active substances ; if the polarised ray 

 passes through the substance" in the opposite direction, the rota- 

 tion still occurs in the same sense as before. This characteristic 

 sharply distinguishes the rotation due to optically active sub- 

 stances from that produced by the magnetic field, the latter 

 rotation being reversed on reversing the direction of the 

 polarised ray. 



Optically active substances may be divided into two classes. 

 Some, like quartz, sodium chlorate, and benzil, produce rota- 

 tion only when in the crystallised state ; the dissolved (or fused) 

 substances are inactive. Others, like oil of turpentine, cam- 

 phor, and sugar, are optically active when in the liquid state 

 or in solution. In the former case the molecules of the sub- 

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

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

 build up a spiral staircase — an asymmetric figure — from sym- 

 metric bricks ; when the staircase is again resolved into its ' 

 component bricks, the asymmetry disappears. (I will explain 

 presently the precise significance of the terms symmetry and 

 asymmetry as used in this connection. ) In the case of com- 

 pounds which are optically active in the liquid state, the 

 twisted structure must be predicated of the molecules them- 

 selves ; that is, there must be a twisted arrangement of the 

 atoms which form these molecules. 



The earliest known experimental facts regarding the rotation 

 of the plane of polarisation by various substances, solid and 

 liquid, were discovered by Arago and by Biot. 



After this preliminary statement as to what is understood by 

 optical activity, we may consider Pasteur's special contributions 

 to the solution of the problems involved. 



Pasteur tells us, in the well-known " Lectures on the Mole- 

 cular Asymmetry of Natural Organic Products," which he 

 delivered in i860, before the Chemical Society of Paris, that 

 his earliest independent scientific work dealt with the subject 

 of crystallography, to which he had turned his attention from a 

 conviction that it would prove useful to him in the study of 

 chemistry. In order to perfect himself in crystallographical 

 methods, he resolved to repeat all the measurements contained 

 in a memoir by De la Provostaye on the crystalline forms of 

 tartaric acid, racemic acid, and their salts. These two sets of 

 compounds have the same composition, except that they fre- 

 quently differ in the number of molecules of water of crystallis- 

 ation which they contain ; but whereas tartaric acid and the 

 tartrates are dextro-rotatory, racemic acid and the racemates 

 are optically inactive. It was probably this circumstance that 

 decided Pasteur in his choice of a subject, for it appears that, 

 even as a student, he had been attracted by the problem of 

 optical activity. In the course of the repetition, however he 

 delected a fact which had escaped the notice of his predecessor 

 in the work, accurate observer as the latter was — namely, the 

 presence, in the tartrates, of right-handed hemihedral faces, 

 which are absent in the racemates. Hemihedral faces are such 



