PHYSIOLOGY

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PHYSIOLOGY (from <pi<<ng, nature, in every sense, and Xoyog, science). This word, first used, as it appears, by Aristotle, would signify, according to its etymology, the science which treats of all the phenomena of nature, the whole universe, and thus would comprise natural philosophy as well as natural history; but the term has been subjected to some restrictions, and is used, sometimes, for the science which treats of all the phenomena of living bodies, and thus becomes synonymous with biology; sometimes for the science which treats of animal life, and then is synonymous with zoonomy, or dynamology; and sometimes for the science which treats of* Physiognomy and phrenology, in a certain degree, always have existed and will exist. Though our rules for judging of men from their appearance may often fail, we still continue to trust in them. We cannot help considering it strange if a sulkylooking man is found to be kind, and a stupidlooking man to be sagacious. We find in the autobiographical letters of the philologer Jerome Wolf (who died 1580), a curious story, that the physician attending his father on his deathbed, looking at the forehead of young Jerome for some time, consoled his father by the assurance that his son would be, at some future time, a capable man, though he might then appear awkward and dull.H. Wolfti de Vitce sum Raiione,&Lc., communicated in Raumer's Historisches Taschenbuck. the phenomena of life in man, and then it corresponds to one of the significations of anthropology. The most scientific use of the word is that which applies it to the phenomena of life in general, as all the phenomena of life, animal or vegetable, are intimately connected with each other. The science would then include vegetable physiology, animal physiology, and comparative physiology, which corresponds to comparative anatomy, and examines the analogies and differences presented by the organic activity of the two classes of beings. Physiology has been further divided into general and special, the former analysing the phenomena of life in an abstract manner, without making the application to particular species, whilst the latter examines the mechanism and the results of life in certain species. Physiology, finally, has been treated under the subdivisions of hygienic, pathologic and therapeutic physiology. As long as these divisions serve simply to assist the student, without conveying wrong ideas as to the science and the subject which it treats, viz. life, so various in its manifestations, yet one and the same throughout all nature, they may be useful. As man stands highest in the scale of beings which we have an opportunity to observe, he is the most interesting subject of physiology, both because animal life is most developed in him, and because his animal life is intimately connected with his intellectual and moral life , for, whatever may be the belief respecting the state of the soul before or after our existence on this earth, it is certain that during the time of our earthly life, the soul and body are, in more than one respect, intimately united. Under this view several German philosophers have treated physiology, and attempted to draw from it illustrations for the higher anthropology. Without going into that subject at present, we shall give here a brief outline of the German mode of treating physiology, which is probably less familiar to our readers than that of France and England. The human frame consists of a multiplicity of organs, which are constantly in a state of mutual excitement and mutual restraint. The chain of causes and effects is endless, yet observation has discovered certain series and orders, called systems. Thus we have the systems of reproduction, irritability and sensibility, (q. v.) The province of the reproductive system is to preserve and unfold the organization. Matter is in uninterrupted change: it undergoes a constant union and separation. This is as true of the animal frame as of the lower forms of matter. There is a constant succession of states, and the whole life of the organization consists, as it were, of innumerable smaller circles of life, beginning with that of the simple substances, each of which runs through certain changes, and then begins anew, and proceeding thence to the higher organs and systems. This constant change in the animal frame requires a constant introduction of new matter into the system, and a constant separation of that matter which has completed its brief tour of duty, and must be thrown off as useless. The new matter received has to undergo a series of changes to adapt it to the purposes of animal life. These changes are effected by means of a number of organs, whose form, construction and activity correspond to their destination. These are the organs of ingestion and digestion, the mouth, throat, stomach and intestines, the absorbing vessels of the intestines, which in their course form glands, then canals, ending at last in one canal. (See Chyle, Digestion, and Dyspepsia.) The received matter becomes purer and purer, that is, fitter for animal life, and eventually becomes blood (q. v.), which change is effected in the lungs (q. v.), from which the blood collects in the left cavities of the heart. (See Heart for an account of the circulation of the blood.) The blood is a fluid endowed with life, and is spread all over the organization, diffusing new matter and life in innumerable currents. The arterial system penetrates every organ, and every organ gives to the matter thus received its peculiar character. Part of this blood, in the shape of coagulated fibres, assumes the first organic form, the cellular texture (an animal crystallization, as it were), attaches itself to the already existing matter of the same kind, in order to assist the latter, if it is yet in the process of formation, or to supply the place of that whose virtue is exhausted^ and, by further processes, gives rise to the various other parts of the human body, as the cellular texture, the various membranes, glands, hairs, bones, cartilage, muscles, arteries, the capillary system, nerves, brain, &c. These single parts, by various combinations, form the compound organs, whose functions vary with their composition. Another part of the blood is destined to be changed into various fluids; this is effected by the function of secretion,* for which several organs are destined. To these belong the secretion of the saliva in the salivary glands, of the gastric juice in the stomach, of the gall in the liver, milk in the breasts, of the mucus in the mucous membranes, &c. After the various forms of organic matter have run through their short circle of life, they lose their character of animal life and activity, change their peculiar form, are dissolved, absorbed in proper canals, and thrown out. This is done by the absorbing lymphatic vessels, by the kidneys and urinary passage, the skin, &c. The system of irritability (q. v.) is composed of the fibre formed out of the blood, and endowed with a higher life, and consists of the muscular fibre, which possesses the faculty of shortening itself by contraction. Aggregations of these fibres form a muscle. Some of these are hollow muscles, for the reception and transmission of fluids, as the heart and the muscular membranes. The others are connected with the system of bones, and serve for voluntary motion. (See Muscles.) The system of sensibility consists of the matter in the highest stage of life, and forms the whole system of the nerves. (See Nerves, and Brain.) These systems are closely connected, and are combined in each organ ; thus we find every where cellular texture, membrane, vessels, &c, and nerves which diffuse a higher life throughout the organs, and produce, by their general connexion, a harmony in the functions of all the organs, which, if undisturbed, is called health. To the series which gives rise to this harmony of the functions belong also the activities of the soul, in so far as the material organization influences them, or the soul influences the material organization. For, though the life of the soul is superior to the life of the body,the latter only following unchangeable laws of nature, the former being guided by reason and volition,yet the close union of both, and their mutual operation, cannot be denied. The material organization affects the soul by the cerebral system and nerves, the soul receiving ideas of outward things through the senses (see Nerves); and though the cerebral system belongs peculiarly to the soul, yet it is nourished and maintained by the same means as the whole animal organization; and this circumstance, and perhaps the connexion of the nerves of the systems of sensibility and reproduction, give rise to what we call instincts and impulses connected with the physical wants. Further, there seems to exist a constant yet silent influence of the material organization on the higher nervous system and the brain, owing the support of these organs by the blood, and to the connexion in which all organs are kept through the nerves; and these circumstances appear to explain the causes of the various temperaments and the change in our dispositions. The soul, on the other hand, operates upon the bodily organization by many voluntary acts, which affect the organic life, by the restraint of the appetites, and by the activity which its own operations necessarily excite in its organ, the brain; and, finally, by the direct influence of certain passions and emotions, on particular parts of the frame. All these points are minutely treated in physiology. The history of physiology is intimately connected with that of medicine. It began with scanty materials and hypotheses. Hippocrates had but a very imperfect knowledge of the human organization, and very limited views of the origin of life. Galen, possessing a better knowledge of anatomy, composed a better system of physiology. From him originated the division of the functions into vital, animal and natural functions, which has maintained itself down to our time. After the middle ages had gone by, the more thorough study of anatomy led to a better system of physiology. Harvey's discovery of the circulation of the blood was a great step, but it induced his successors to attempt to explain life by mere mechanical and hydraulic principles. Stahl (q. v.) considered the soul as the cause of life and its phenomena ; but Haller made an entirely new epoch, by the theory of the irritability of the fibre, which was made the basis of many systems; even Brown's theory of life, as arising from the irritability of the organization, and the influence of external things, is to be deduced from this source. The progress of chemistry and philosophy gave rise to another mode of treating physiology, the former by analysing the simple substances of the body, the latter by the faithful investigation of what is within and what without the limits of the reasoning faculty, thereby banishing a number of untenable theories.