PHYSIOLOGY 485 effervescence and fermentation of the fluids, entirely excluding the solids from his physio- logical scheme ; food fermented in the stomach under the influence of the gastric fluids, and digestion was perfected by the actions estab- lished by the addition of the bile and the pan- creatic secretion ; the movement of the blood in the, heart was due to the effervescence ari- sing from the meeting of an oily volatile salt of the bile with a saccharine acid of the lymph, producing at the same time the animal heat; the vital spirits, entirely material, were pre- pared in the brain by distillation, having much of the properties and nature of alcohol; all diseases were caused by the predominance of this or that chemical element in the fluids, and to counteract a supposed acidity very power- ful chemical preparations were rashly admin- istered. While Sylvius taught these doctrines upon the continent, Willis promulgated similar ones in Great Britain ; he also made the chyle effervesce in the heart under the influence of salt and sulphur, which took fire together and produced the vital flame. According to Haller, even the great mind of Newton was led astray by such vagaries as these. Many of the popular ideas of peccant humors, for which a multitude of empirical remedies are continually extolled and exhibited, date back to the chemical theories of the 17th century. Boerhaave and his school, early in the 18th century, substituted mechanical for chemical forces in physiology, explaining the pheno- mena of life on the principles of mechanics and mathematics, according to the idea of Des- cartes. The then admitted doctrine of Harvey of the circulation of the blood and the discov- eries of Galileo favored the progress of this school. Food was reduced in the stomach to minute particles by trituration ; the circulation was a complete hydraulic machine, and the heart a perfect sucking and forcing pump ; the weight of the blood and the loss of its motive power from friction in the vessels were exactly calculated, and the force of the heart's contrac- tion estimated at 180,000 Ibs. ; the differences in the secretions were explained by the diame- ter, foldings, and number of the divisions of the vessels in the secreting organs, and by the diverse forms of the molecules, some of which were admitted and others excluded by these kinds of organic sieves ; animal heat was the result of the friction of the blood globules against each other and against the walls of the minute vessels. Electricity was at one time considered the active agent of the vital func- tions, and certain analogies indeed favored this view ; electricity dethroned the vital principle, and the barrier erected with so much labor between living and inorganic bodies was again thrown down. Glisson, in England, toward the middle of the 17th century, while the phys- ical theories of life were in vogue, maintained the activity of matter, and that all the func- tions of life depend on a property of living animal substance which he calls irritability, entirely independent of physical or mechanical forces all parts of the body, even the bones and the fluids, possessing this property. This theory was completely forgotten until toward the middle of the 18th century, when various authors made use of the terms contractile force and tonicity. Haller (1747) admitted two prop- erties, irritability and sensibility (vis insita and ms nervosa). This irritability is the property of contracting under stimuli (the will for the ordinary muscles and their contents for the hollow ones), now styled contractility, distinct from and more powerful than elasticity, in- dependent of the nervous force, and improp- erly called vital inasmuch as it is manifested after death. Sensibility is the power of per- ceiving the impressions derived from contact. This theory gave a great impulse to physio- logical science, which before this was in a very confused state. Barthez, in the last half of the 18th century, adopted the phrase vital principle, which he regarded as distinct from the soul, and as having its own proper exis- tence and its motor and sensitive forces, the former residing in the muscles, the latter in the fluids and especially in the blood ; this system met with great favor. Bichat, a quarter of a century later, reduced the vital properties to two, contractility and sensibility, each divided into the animal or voluntary and the organic or involuntary. Brown, a few years before this, had elevated the property of excitability in the tissues into the vital principle; according to him, all diseases are either sthenic or asthenic, the vital force being increased in the former and diminished in the latter; the doctrine gave rise to the contra-stimulant practice of Rasori and others. Blumenbach, toward the end of the 18th century, attributed all the formative actions to a force which he called nisus forma- tions. Broussais, early in the 19th century, made pathology a branch of physiology, and gave to his system the name of physiologi- cal doctrine of disease ; his celebrated theory placed essential fevers among the inflamma- tions of the digestive tube, as forms of gastro- enteritis. Gerdy admitted 17 vital principles, or so many distinct series of phenomena inex- plicable by physical laws, a list which on his principles might be very greatly and incon- veniently extended. Modern physiology rec- ognizes the fact that many of the phenomena presented by living bodies are purely physical or chemical, and are to be studied by pre- cisely the same methods as any other phys- ical or chemical phenomena. Such are the mechanism of the joints and the movements of the limbs upon the trunk ; the extent, force, and rapidity of muscular contraction in gen- eral .; the changes which take place in the food during digestion and in the air during respira- tion ; the exhalation and imbibition of various matters by the blood vessels in the course of the circulation; the pressure and velocity of movement of the blood itself, and its changes of color and constitution. Not that these
