Without waiting for new facts, those already in our possession tend, I think, to render the association which M. Pasteur seeks to establish between dissymmetry and life insecure. Quartz, as a crystal, exerts a very powerful twist on the plane of polarisation. Quartz dissolved exerts no power at all. The molecules of quartz, then, do not belong to the same category as the crystal of which they are the constituents; the former are symmetrical, the latter is dissymmetrical. This, in my opinion, is a very significant fact. By the act of crystallisation, and without the intervention of life, the forces of molecules, possessing planes of symmetry, are so compounded as to build up crystals which have no planes of symmetry. Thus, in passing from the symmetrical to the dissymmetrical, we are not compelled to interpolate new forces; the forces extant in mineral nature suffice. The reasoning which applies to the dissymmetric crystal applies to the dissymmetric molecule. The dissymmetry of the latter, however pronounced and complicated, arises from the composition of atomic forces which, when reduced to their most elementary action, are exerted along straight lines. In 1865 I ventured, in reference to this subject, to define the position which I am still inclined to maintain. 'It is the compounding, in the organic world, of forces belonging equally to the inorganic that constitutes the mystery and the miracle of vitality.'[2] Add to these considerations the discovery of Faraday already adverted to. An electric current is not an organism, nor does a magnet possess life; still, by their action, Faraday, in his first essay, converted over one hundred and fifty symmetric and inert aqueous solutions into dissymmetric and active ones.[3] Theory, however, may change, and inference may fade away, but scientific experiment endures for ever. Such durability belongs, in the domain of molecular physics, to the experimental researches of M. Pasteur. * * * * * The weightiest events of life sometimes turn upon small hinges; and we now come to the incident which caused M. Pasteur to quit a line of research the abandonment of which he still regrets. A German manufacturer of chemicals had noticed that the impure commercial tartrate of lime, sullied with organic matters of various kinds, fermented on being dissolved in water and exposed to summer heat. Thus prompted, Pasteur prepared some pure, right-handed tartrate of ammonia, mixed with it albuminous matter, and found that the mixture fermented. His solution, limpid at first, became turbid, and the turbidity he found to be due to the multiplication of a microscopic organism, which found in the liquid its proper aliment. Pasteur recognised in this little organism a _living ferment_. This bold conclusion was doubtless strengthened, if not prompted, by the previous discovery of the yeast-plant--the alcoholic ferment--by Cagniard-Latour and Schwann.