Four-and-twenty centuries ago, Hippocrates, the father of medicine, gave to the world his celebrated treatise, _de aere, aquis et locis_ περι ὑδατων αερον και τοπων, having for its object an inquiry into the influence of the external world on man’s physical structure and moral nature. To trace the origin of disease to these circumstances, does not seem to have fallen within the scope of his argument; accordingly, it can scarcely be said that any author prior to Macculloch ever considered this matter from a philosophical or physiological point of view, a reason for which may be found, I think, in the absence of a minutely accurate chemical analysis of natural and artificial products. No Ehrenberg had taught mankind the wonders of the living microscopic world of life; even the geology of Macculloch was much behind the profound analyses of the present day. Sober thinking men had rejected the bold speculations of Buffon as to the antiquity of life on the globe, and the demonstrations of the immortal Cuvier were as yet but partially admitted; whilst the theories of Lamark, respecting the vast influence of life in the construction of the crust of the globe, had been suffered quietly to fall into abeyance. Life was thought to be but a recent acquisition by the earth; the Silurian and Cambrian systems of fossils were either unknown or misunderstood. These fossils, at present called “the first stages of this grand and long series of former accumulations,” must, in the nature of things, yield their claims to others which geology will no doubt soon discover, thus rendering more than probable the theory that life and the globe are coeval.