Page:The Harveian oration 1903.djvu/48

 "possess, in a much greater degree than those of any other element, the property of combining with similar atoms whereby a part of their valencies are satisfied." Thus may be formed groups of carbon atoms so linked together that their valencies are in part satisfied among themselves, constituting what are known as carbon nuclei; and the free valencies being satisfied by atoms of other elements molecules are formed in which much energy is accumulated with more or less instability.

Such conceptions as to the fundamental nature of matter, of its molecular structure and arrangement of atoms therein, permitted the laying down of rational or structural formule for chemical compounds; and when the further suggestion was made of linking the atoms in tridimensional space rather than in a single plane a still further extension of the idea of the atomic disposition within the molecule became possible and " stereo-chemistry was born" (Clarke).

With theories of this kind ready at hand, theories which had done and are still doing so much to explain the phenomena met with in the domains of physics and chemistry, what more natural than that the biologist, recognising that but little progress was being made in the