PHYSIOLOGY

(Yunanca köken — orijinale bakınız.) 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 Enghsh 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 defined had not been sanctioned by philosophers of other nations. 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 definition 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 b^ the veins. With respect to this chief manifestation of life in the torpid animal it may be asked. What is th« 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? 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 usele principles, through the excretion of the kidneys, and of tlie 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, exec ret i on, 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 phenomena of irritability and contractility of muscular fibre are superadded, as in the action of the heart; and this is dependent on the connection of the muscular fibre with a nerve. The power of the external decomposing forces is increased by elevation of temperature; and the stimulus of heat produces in the torpid animal, in a manner not understood, a reaction 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 contact with the thin membrane over which the pulmonary capillaries are richly spread. The result of this contact is the immediate elimination of the carboc [s. 939]