PHYSIOLOGY, according to the modern' use of the term, may be defined, the science which treats of the functions of the living animal body, and of the powers upon which these functions depend.
Although it is impossible to enter into any speculations, either medical or pathological, without presupposing a certain acquaintance with the operations of the body in its healthy and natural state, yet the contrary plan has been pursued in the medical sciences. Until about the middle of the last century, we had no writers who made phy siology an exclusive, or even a direct object of their atten tion; so that we are to collect our information, respecting the hypotheses or opinions that were entertained before that time, from the incidental notices or observations that occur in works written professedly either on pathology, or on the practice of medicine. As we have given a sketch of the authors of this description in the history of MEm crNE, we shall refer to this article for an account of the physiological opinions and hypotheses of the earlier wri ters; and shall, in this place, only offer a few remarks upon the progress of the science from the period when it was brought before our notice, as a distinct department of natural philosophy, by Haller.
This celebrated individual is, in every point of view, entitled to be considered as the father of modern phy siology, whether we regard the unremitting assiduity with which he cultivated the science, or the actual advance ment which he effected. Every circumstance, both of talent, character, and situation, conspired to promote his great object; in learning, in industry, in discrimination, and in candour, he has seldom been excelled; lie devoted a large portion of his life to the cultivation of physiology, while his rank and fortune gave every facility to his exer tions. What, however, more especially entitles him to the highest commendation, is the method which he intro duced and established, of investigating the phenomena of the living body solely by observation and experiment, and keeping hypothesis entirely in subjection to these two leading principles. So powerful an effect have his influ ence and example produced, that, since his time, the sci ence has assumed altogether a different aspect ; and, from the publication of his " Elements," we may date the com mencement of a new era in physiology.
'This great monument of learning and industry was still in progress, when Cullen entered upon his career; a man of a very different, and, in some respects, of an almost op posite turn of mind, yet one who was eminently useful in this department of knowledge. Ile excelled in general
views rather than in minute researches; and, without adding many new facts to our previous stock of informa tion, he arranged, into a very beautiful and interesting system, those of which we were already in possession. Few persons have contributed more than Cullen to sweep away the useless rubbish of antiquity ; and there is a spirit of philosophical scepticism that pervades his writings, which, very fortunately, coincided with the inquiring genius of the age in which he lived.
Among the authors who have been most successful in the cultivation of this branch of science, we arc necessa rily led to class John Hunter. He possessed a remarkable share of boldness and originality of conception; and, in addition to these qualities, he manifested the most patient industry in the examination of nature under all her forms, and under every aspect in which she presents herself to our notice. He professed to proceed entirely upon the result of experiment and observation; but, in this respect, lie exhibited an example of self-deception which is by no means rare, for his writings arc, in fact, full of hypothesis, and abound with theories expressed or implied. He has unhappily introduced into physiology a kind of metaphy sical language, which has certainly tended to impede the progress of science, by substituting new expressions for new ideas, thus leading us to suppose that we had made an addition to our knowledge, when, in fact, we were merely employing new forms of speech. Upon the whole, however, since the time of IIaller, there is, perhaps, no one to whom the science is more indebted than to Hunter for important facts; and upon these his fame will be am ply supported when his speculations are forgotten. In all his physiological hypotheses, Hunter makes perpetual re ference to the existence and energy of what lie calls the vital principle. It is not easy, on many occasions, to de termine how far his expressions are to be received in a literal, or how far in a metaphorical sense, but many of then) strongly resemble the Stahlian doctrine, of an intel ligent principle, connected with the body, directing its motions, and preserving it from injury or destruction. In his explanation of the functions and operations of the living animal, he not unfrequently confounds physical with final causes, and attributes to the specific effects of life, actions that ought to be referred to the powers belonging to inanimate matter.