Until experimental philosophy and inductive reasoning shall be separated from fanciful and hypothetical speculations, the science of medicine can meet with but slow success. And as we have not all the advantages attendant on the other physical sciences, having the operations of a living machine, if I may use the expression, to calculate, we must be content to move with a slower step. Nor must we commit our barque to the full and easy flowing stream of conjecture and hypothesis. Conjectures are ever vague and hypothesis seldom leads to the discovery of truth. Some physiologists, and those of no mean note, have considered the operations of the human frame as a circle of functions governed by mechanical organic laws, as we discover in an hydraulic machine, or automaton, so admirably formed, as by the mere force of its construction to perform and continue the vital motions. In confutation of such an opinion we have nothing to do more than to introduce the words of the justly celebrated Doct. Whytt. “It seems” (says that writer) “to be incumbent on those philosophers who ascribe the motion of the heart to mechanical causes alone, to demonstrate the possibility of a perpetuum mobile, since as long as life lasts, an animal appears to be really such.” And it needs scarcely be added that perpetual motion is demonstrably without the laws of mechanics, and far above the power of mechanism. These considerations are, I judge, sufficient to put to rest all idea of an independent _organic_ life: If others are wanted, it may be shewn that life, sense, and self-action, are inconsistent with the general properties of matter. Others, writers of much reputation and celebrity, have contended for the existence of an innate independent principle of life in the muscles, and the plausible ingenuity with which these opinions were supported, could not fail to procure many advocates, and has indeed enlisted in its cause such a body of respectable talents, as to induce me to hesitate in my intended opposition: Nor do I now venture presumptuously to undertake the settlement, but shall only offer such reasons in objection to the doctrine, as have been suggested by various circumstances. It is not my intention to engage in all the minuteness of particular discussion. That would require more time and attention than I can at present devote to such an undertaking; but I shall content myself by briefly stating all the arguments which have fallen within my reading, most insisted on by the strenuous defenders of the above doctrine, and on which alone it seems to rest.――Then, by considering the arguments separately, endeavour to shew wherein they are fallacious, and point out the difficulties calculated, in my opinion, to oppose such specious reasoning. The punctum saliens, or the first visible point in motion being the heart; The birth of full grown Fœtuses without brains; The performance of vital motions without consciousness;