After these verifications and deductions from theoretic views, Pasteur discovered a surprising connection between the prior researches of chemistry and crystallographic physics and the new and entirely unexpected results of physiological chemistry. This connection, like the thread of Ariadne, conducted him to his recent great discoveries in medical biology. M. Chevreul was right when, some years ago, at the Academy of Sciences, he expressed himself thus:-- 'It is by first examining in their chronological order the researches of M. Pasteur, and then considering them as a whole, that we are enabled to appreciate the rigour of judgment of that learned man in forming his conclusions, and the perspicacity of a mind which, strong in the truths which it has already discovered, is carried forward to the establishment of new ones.' III. Pasteur had thus established that bodies endowed with internal dissymmetry carried this property, in varying degrees, into their compounds or their derivatives. When two of these bodies whose nature has been revealed by the discovery of right-handed and left-handed tartaric acid, where all is chemically identical--and which are only to be distinguished from each other by their inverse crystallographic form, and by their action on polarised light--enter into combination with a substance which is optically and crystallographically inert, the chemical identity ought, under these new conditions, to be preserved. Everything remains optically and crystallographically comparable. The inert element adds nothing to, and takes away nothing from, the dissymmetric faculties of the active one. To these curious studies Pasteur soon added a new chapter. He reasoned thus:--If into these compounds I introduce a substance possessing in itself the specific properties of dissymmetry, it is evident that this substance, while entering into these combinations, must preserve its own properties. The active substance would, from the moment of its combination, add something to the properties of the molecular group which acts like itself, and subtract something from the properties of the group which acts in the opposite manner. The resultant effect of these actions, sometimes concordant, sometimes antagonistic, would cease to be alike in absolute quantity. And if this be the necessary condition of similitude as to molecular arrangement, this similitude would cease to exist, and with its disappearance would appear all the differences of chemical and physical properties which constitute its outward manifestations. The facts were found to harmonise with these logical deductions. After having made dissymmetry intervene as a modifier of chemical affinity, he had a strange and manifest proof of the influence of dissymmetry in the phenomena of life.