(From the principal, chief, or first mover). The supposed primum mobile of Helmont, which, in his opinion, superintended the animal economy, and preserved it. It resembles Plato's anima mundi. Hippocrates uses the words to signify the former healthy state before the attack of the disease. It is also a term coined by Paracelsus; by it he would express the sole active principle in the material world.
But however language has diversified the nature and operation of this principle, the existence of a power in the animal system, to correct accidental deviations from health, and to preserve the body in a sound state, is undeniable. When nature is said to act, such a principle -must be intended. Van Helmont, who, among numerous fancies, possessed in many instances a sound judgment and extensive knowledge, placed his archaeus in the stomach, and supposed it the grand regulator of the animal machine. Stahl adopted the principle, and extended its influence, without however fixing its throne in any one part. The system of Stahl was widely diffused in Germany, and for a long time obscured the humbler, but scarcely less industrious, labours of Hoffman; and to Stahl, Dr. Cullen has been more indebted than is generally supposed, or he was himself willing to acknowledge. The great point at issue between the disciples of Van Helmont and Stahl, and the more modern physiologists, is the action of this principle. Stahl contended, that nature acted from wide extensive views, consulting with consummate wisdom the good of the machine entrusted to her care. Dr. Cullen, while he admitted the benefits produced by the operations of nature, considered her action as the necessary consequence of immutable laws; and denied that we in any instance possessed a power of acting, directed by means; chiefly since these means were beyond our knowledge; nor were we in many instances conscious even of the end or object. We need not expand this article by the arguments on either side. In the works of Stahl, particularly in his ' Theoria Medica Vera,' and in the theses, published by his pupils, the whole doctrine is expanded with singular ingenuity, and supported with a logical precision, of which, in the annals of medicine, there is no example or imitation. It is more clearly explained in the works of Junker; for the language and the laboured precision of Stahl place him beyond the reach of many readers. As the principle is acknowledged, we ought to look to physiologists for its explanation: none has, however, been offered, except that hinted at above by Dr. Cullen. The power evidently does not reside in the immaterial principle, but is the result of changes more purely material; and such is the constitution of the animal machine, that, by being repeated, it obtains greater facility of action. Nature, then, often urged to supply deficiencies and correct deviations, acts more readily, and performs her office more successfully. In a future part of this work we shall resume the subject; and when the articles to which we must refer are before the reader, we may make some advances in the explanation. See Vires naturae'.