As a subject for my inaugural dissertation, I am induced rather to offer some general opinions on the state of the animal system, than to enter into particular disquisitions on given points. The time allotted, in general, for the production of inaugural essays, and the peculiar circumstances under which I have to write, preclude the hope of my advancing the science of medicine; I am therefore chiefly anxious not to embarrass its progress by hasty conclusions or fanciful chimeras. The opinions I have thought proper to bring forward are advanced with as much perspicuity and order as my application to other engagements would permit; and although they are founded, I trust, on manifest facts or inductions from established propositions, still I must submit them with diffidence: and should the ground, I have taken, prove untenable, I have to regret that my opportunities have not placed me on a more advantageous stand. THESIS. The capacity and aptitude for motion, observable in man, naturally lead us to an enquiry into the general principle of his corporeal functions. To a disquisition of which I devote the following pages. Aware of the intricacy of my subject, and that the operations of the animal body necessarily embrace agents not within the range of our senses, I cannot indulge in the hope that I shall be altogether successful in an examination of the laws of its economy. Where so many enlightened and able intellects have labored in vain, it would require an excess of vanity in me to expect to succeed; and, I trust, should I leave some of the difficulties unsurmounted and inequalities unsmoothed, I shall not be fairly chargeable with temerity or indiscretion. Amidst our contemplation of the various simple and compound actions, of which the human body is capable, and in which it is perpetually engaged, we are unavoidably led to ask――whence is the peculiar power or capacity, so admirably diffused throughout its numerous parts, by which those actions are performed? Is it by any peculiarity of organization? or by properties different according to the nature of the various constituent parts? or a particular principle, not strictly inherent in any one part, but diffused to all? It cannot be in the organization, although it does not manifest itself without organization, for, if so, there would uniformly be a difference between the texture of dead and living parts, which frequently is not the fact. Nor have we full and satisfactory evidence on which to found the opinion that it is owing to properties differing in their essential natures according to the parts concerned. That the principle of life or capacity of acting, or being acted on, is strictly the property of one part, and is by diffusion communicated to the rest, we have much reason to conclude from the phenomena of both health and disease.