PHYSIOLOGY

(Gr. (pvais, and \oyo$, a discourse.) The science of things generated or alive; but usually regarded as the doctrine of vital phenomena. This science is divided, according to the two great cla es of generated beings, into animal and vegetable physiology. Some philosophers have proposed to change the term for " biology;" but the restricted application of bios to the life of an individual in other English compound words, as "biography," would be an objection to this change, even if the word physiology were le appropriate than it is, or if its use in the sense above other nations.defined had not been sanctioned by philosophers of The chief object of the physiologist is to ascertain the precise mode in which each part or organ of a living being reacts when stimulated. When the precise conditions and mode of the reaction of the circulating fluid upon the solids, and reciprocally, are understood, a true and intelligible defi nition of life may, perhaps, be given. In animal physiology, the simplest condition under which life can be contemplated is that which it presents in the torpid hybernater. • During this state a dark nutrient fluid, the venous blood, (see Blood), is propelled, by the contractions of a hollow muscle (see Heart), along the arteries to every part of the body, whence it is again returned to the heart by the veins. With respect to this chief manifestation of life in the torpid animal it may be asked, What is the cause or condition of the reaction of the fibres of the hollow muscle upon the stimulating fluid? How does each ti ue of the body select from the currents flowing through the terminal capillaries the appropriate particles for its growth or reparation, and, in return, add to the blood, either directly or through the medium of lymphatic ve els, its effete particles 1 These are questions which physiology has yet to resolve: the electric conditions of the parts concerned have not been ascertained. The blood is maintained in a fit state for the preservation of the ti ues of the torpid animal by slowly parting with some noxious or useles principles, through the excretion of the kidneys, and of the different mucous and serous surfaces. The reaction of the circulating fluids upon the solids supersedes the ordinary chemical reaction, by which they would be decomposed and destroyed, and thus the torpid animal is kept alive; but it is the life of the plant or of the ovum. The functions of circulation, nutrition, execution,are manifested when life is thus reduced, as in the plant, to its simplest condition; and these must, therefore, be its most e ential actions. In the torpid animal, the phe nomena of irritability and contractility of muscular fibre are superadded, as in the action of the heart; and this is dependent on the connexion of the muscular fibre with a nerve. The power of the external decomposing forces ia increased by elevation of temperature; and the stimulus of heat produces in the torpid animal, in a manner not understood,are action of the mucous surface of the lungs: this reaction influences, through the nerves, the muscles of respiration,and atmospheric air is inspired and brought into with the thin membrane over which the pulmonary are richly spread. The result of this contact is immediate elimination of the carbon from the blood, changes its dark for a florid red colour; or converts from venous to arterial blood. The blood, so changed, stimulates in a different and more manner the parts over which it is distributed; the contracts more vigorously and frequently; the brain nervous system now receiving more blood, and that of different kind, begin to react on the application of stimuli which they were before insensible. First, self-consciousne ; then sensation of external impre ions lastly,; the propagation of a stimulus to the system generally, which produces the reaction vibratile contraction of its fibre, and by which the animal moves its parts upon each other, or its entire body upon matter, are succe ively manifested; and to circulation, nutrition, excretion, and respiration, are now added functions of sensation and voluntary motion. But with greatly increased activity of the whole organic machinery, there is a proportional increase of vital decomposition;t.e., of abstraction by the ti ues of a imilating from the capillary blood, and of addition to the of effete particles; and those actions demand not increased activity in the organs which eliminate the and noxious particles from the blood, and expe! them the body, but also a means of supplying new iiond [s. 946]