Λεγέτω μὲν οὖν περὶ αὐτοῦ ὡς ἕκαστος γιγνώσκει, καὶ ἰατρὸς, καὶ ἰδιώτης, ἀφ’ ὅτου εἰκὸς ἦν γενέσθαι αὐτὸ, καὶ τὰς αἰτίας ἅστινας νομίζει τοσαύτης μεταβολῆς ἱκανὰς εἶναι δύναμιν ἐς τὸ μεταστῆσαι σχεῖν. And now I leave every one, whether physician or not, to pass his own opinion concerning it, pointing out whence it was likely to arise, and what causes he thinks sufficient to produce so entire a change in the constitution of the human body.”--(Thucydides on Epidemics.) CHAPTER XII. PROPHYLAXIS: OR THE MODE OF PREVENTING DISEASE. “Organic forms with chemic changes strive, Live but to die, and die but to revive; IMMORTAL MATTER braves the transient storm, Mounts from the wreck, unchanging but in form.” The original mandate of the Creator has provided that by various natural processes a constant equilibrium shall be preserved and maintained, so that from age to age, until all the purposes for which the earth is sustained be completed, the same ends will be accomplished by the same agency: “That very law which moulds a tear And bids it trickle from its source, That law preserves the earth a sphere, And guides the planets in their course.” We further know that all organized matter, whether animal or vegetable, possesses the materials of which they are composed, for a limited time only, life itself being but a boon, lent to serve the purposes of Infinite Wisdom-- “Which thus alternating with death fulfil The silent mandates of the Almighty’s will; Whose hand unseen the works of Nature dooms, By laws unknown;--who gives and who resumes.” Again, on reviewing the histories of bygone ages, we learn that from the earliest times disease has visited every country with a frequency and malignancy always proportioned to the intensity of the predisposing causes. Under the head of Nature and Causes of Disease, I have already advanced that disease arises from certain conditions or vicissitudes of the atmosphere, together with the application of other powers producing direct debility. Over the former, as the exciting, the vital cause, we have but little control; it is the latter only, the predisposing causes, that we can attempt to counteract with a fair prospect of success. Seeing that such predisposing causes more generally arise from the infraction of the unalterable laws originally laid down for the government of mankind,--from a neglect of the most obvious laws of our being,--and that Providence, for the most part, acts by SECONDARY CAUSES, we should direct our efforts to the arresting of every condition which _predisposes_ to or aggravates disease, such condition being more or less subject to human regulations.