814 REPORT— 1898. 



so that their doctrines contradicted the law of the consevvatioa of energy, and 

 became untenable the moment that this law was established. T 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. Professor 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 tlie 

 organism to account for the actual day by day expenditure of heat and work,' lie 

 does not consider this special case. Tne application of the foregoing principle 

 of dynamics to the discussion of problems like the present is, I believe, due to the 

 late Professor Fleeming Jenkin. A third ground for abandoning the doctrine of a 

 'vital force' was the discovery that numerous organic compounds for the pro- 

 duction 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 

 vieVs ; these arguments and the facts on which they are based lie entirely outside 

 my province. I shall coutine 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 endeavour to show that living matter is constantly performing 

 a certain geometrical feat which dead matter, unless indeed it happens 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 perform- 

 ing. My argument, being based on geometrical and dynamical considerations, 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 stereochemical research on 

 this physiological problem, it will be necessary to give a brief sketch of the stereo- 

 chemistry of optically active organic compounds, as foimded 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 in said to be dextro-rotatory ; in the 

 latter, laevo-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, 

 lust 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 

 rotation still occurs in the same sense as before. This characteristic sharply 

 distinguishes the rotation due to optically active substances from that produced 

 by thi' 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, 



