Pasteur's discovery was much more than a new fact in chemistry and physics. It was the foundation-stone that was to support the new science of stereochemistry--the study of the physiochemical arrangement of atoms within the molecule--that took its rise a few years later. Much more, it was a great landmark in biology. Pasteur pointed out that all mineral substances--that is, all the natural products not due to living energy--have a superposable image and are, therefore, not dissymmetrical. All the products of vegetable and animal life are dissymmetrical. All these latter substances turn the plane of polarization. This is the great fundamental distinction between organic and inorganic substances--the only one that has endured thus far in the advance of science. Dissymmetry probably represents some essential manifestation of vital force. Often there seem to be exceptions to this law; but careful analysis of the conditions of the problem shows that they are not real. {300} An apparent contradiction, for instance, to this law of demarcation between artificial products and the results of animal and vegetable life is presented by the existence in living creatures of substances like oxalic acid, formic acid, urea, uric acid, creatine, creatinin, and the like. None of these substances, however, has any effect on polarized light or shows any dissymmetry in the form of its crystals. These substances, it must be remembered, are the result of secondary action. Their formation is evidently governed by the laws which determine the composition of the artificial products of our laboratory, or of the mineral kingdom properly so called. In living beings they are the results of excretion rather than substances essential to life. The essential fundamental components of vegetables and animals are always found to possess the power of acting on polarized light. Such substances as cellulose, fecula, albumin, fibrin, and the like, never fail to have this power. This is sufficient to establish their internal dissymmetry, even when, through the absence of characteristic crystallization, they fail to manifest this dissymmetry outwardly.