But when the heat of the battle was over and the bitterness of the strife forgotten, it was found that, although many pinnacles of the dualistic castle had been shattered, the foundation and great part of the walls remained; and, strange to say, the men who led the attack were content that these should remain. The atom could no longer be regarded as always composed of two parts, but must be looked on rather as one whole, the properties of which are defined by the properties and arrangements of all its parts; but the conception of the atom as a structure, and the assurance that something could be inferred regarding that structure from a knowledge of the reactions and general properties of the whole, remained when Dumas and Liebig had replaced the dualism of Berzelius by the unitary theory of modern chemistry; and these conceptions have remained to the present day, and are now ranked among the leading principles of chemical science; only we now speak of the "molecule" where Berzelius spoke of the "atom." Along with these advances made by Dumas, Liebig and others in rendering more accurate the general conception of atomic structure, we found that the recognition of the existence of more than one order of small particles was daily gaining ground in the minds of chemists. The distinction between what we now call atoms and molecules had been clearly stated by Avogadro in 1811; but the times were not ripe. The mental surroundings of the chemists of that age did not allow them fully to appreciate the work of Avogadro. The seed however was sown, and the harvest, although late, was plentiful. We saw that Dumas accepted, with some hesitation, the distinction drawn by Avogadro, but that failing to carry it to its legitimate conclusion, he did not reap the full benefit of his acceptance of the principle that the smallest particle of a substance which takes part in a physical change divides into smaller particles in those changes which we call chemical. To Gerhardt and Laurent we owe the full recognition, and acceptance as the foundation of chemical classification, of the atom as a particle of matter distinct from the molecule; they first distinctly placed the law of Avogadro--"Equal volumes of gases contain equal numbers of molecules"--in its true position as a law, which, resting on physical evidence and dynamical reasoning, is to be accepted by the chemist as the basis of his atomic theory. To the same chemists we are indebted for the formal introduction into chemical science of the conception of types, which, as we found, was developed by Frankland, Kekule, and others, into the modern doctrine of equivalency of groups of elementary atoms.