posed electrical agencies. This view was subsequently abandoned by M. Dutrochet, in favour of the following principle. It is well known that porous bodies, as sugar, wood, or sponge, are capable of imbibing liquids, with which they are in contact. In such case, the liquid is not merely introduced into the pores of the solid, as it would be into an empty space; but it is forcibly absorbed, so that it will rise to a height considerably above its former level. This "osmotic force" is molecular, and is the same that we witness in the phenomena presented by the capillary tube, which affords us the simplest case of the insinuation of a liquid into a porous body. It cannot alone, however, cause the liquid to pass entirely through the body. If a capillary tube, capable of raising water to the height of six inches, be depressed, so that one inch only be above the surface, the water will rise to the top of the tube; but no part of it will escape. Even if the tube be inserted horizontally into the side of the vessel containing water, the water will only pass to the end of the tube. The same thing occurs when a liquid is placed in contact with one side of a porous membrane: it enters the pores; passes to the opposite side, and is there arrested. But if this membrane communicates with a second vessel containing a different liquid-as a saline solution, capable of mixing with the first, and affected to a different degree by capillary attraction-a new phenomenon will be presented. It will be found, that both liquids enter the pores, and pass through to the opposite side. They will not, however, be carried through with the same force: that which has the greatest power of capillary ascension, has the greatest affinity for the membrane, or will wet it more readily,--in other words, that which will rise the highest in a capillary tube,—will pass through in greater quantity, and cause an accumulation of liquid on the opposite side. The action is well shown by the simple instrument figured in the margin. It consists of a glass tube, the lower extremity of which, covered by bladder, is funnel-shaped. This M. Dutrochet termed an endosmometer. If an aqueous solution of either gum or sugar be poured into it, and the closed extremity be immersed in pure water, the water is found to pass continually into the tube by filtration through the membrane, so that the liquid will rise in the tube, and may even flow out at the upper aperture. At the same time, a portion of the mucilaginous or saccharine solution will escape from the tube through the bladder, and become mixed with the water, but the quantity will be much less than that of the water which entered.

Fig. 1.

Endosmo

meter.

The facts and arguments adduced by Dr. Mitchell clearly exhibit, that imbibition and transudation are dependent upon the penetrativeness of the liquid, and the penetrability of the membrane; that if two liquids, of different rates of penetrativeness, be placed on opposite sides of an animal membrane, "they will in time present the greater accumulation on the side of the less penetrant liquid, whether more or less dense; but will, finally, thoroughly, and uniformly mix on both sides; and at length, if any pressure exist on either side, yield to that, and pass to

the other side." In all such cases, there are both endosmose and exosmose--or double imbibition; in other words, a certain quantity of one fluid passes in, and a certain quantity of the other passes out.2 out.2 As a general rule, imbibition takes place from the rarer to the denser medium; from pure water or dilute solutions towards those that are more concentrated. It would appear, again, that the stronger current is always from the medium which has the strongest affinity for the substance of the septum. It is well known, that in the case of a mixture of dilute alcohol covered over by a piece of bladder, the alcohol becomes concentrated, owing to the water--a denser fluid--passing more rapidly through the septum or bladder than the alcohol; but if the same mixture be tied over with elastic gum, the contrary effect will be produced--the alcohol escaping in greater quantity. The general conditions of the phenomena of endosmose are:-first, that the two liquids shall have an affinity for the septum or interposed membrane; and, secondly, that they shall have an affinity for, and be miscible with

each other.

A portion of the communication of Dr. Mitchell relates to an analogous subject, to which, as M. Magendie' has observed, little or no attention had been paid by physiologists-the permeability of membranes by gases. "The lamina," M. Magendie remarks, "of which membranes are constituted, are so arranged that gases can penetrate them, as it were, without obstacle. If we take a bladder, and fill it with pure hydrogen, and afterwards leave it in contact with atmospheric air, in a very short time the hydrogen will have lost its purity, and be mixed with the atmospheric air, which has penetrated the bladder. This phenomenon is more rapid in proportion as the membrane is thinner and less dense. It presides over one of the most important acts of life-respiration; and continues after death."

Dr. Mitchell is the first individual, who directed his observation to the relative penetrativeness of different gases. This he was enabled to discriminate by the following satisfactory experiment, which we give in his own words: "Having constructed a syphon of glass, with one limb three inches long, and the other ten or twelve inches, the open end of the short leg was enlarged and formed into the shape of a funnel, over which, finally, was firmly tied a piece of thin gum elastic. By inverting this syphon, and pouring into its longer limb some clear mercury, a portion of common air was shut up in the short leg, and was in communication with the membrane. Over this end, in the mercurial trough, was placed the vessel containing the gas to be tried, and its velocity of penetration measured by the time occupied in elevating to a given degree the mercurial column in the other limb. Having thus compared the gases with common air, and subsequently by the same instrument, and in bottles with each other, I was able to arrange the following gases according to their relative facility of

1 Amer. Journal of the Medical Sciences for November, 1833, p. 100.

2 Magendie, Le,ons sur les Phénomènes Physiques de la Vie, tom. i. p. 99, Paris, 1836-38.

Henle, Allgem. Anat., or Jourdan's French translat., p. 210, Paris, 1843; and Wagner, Elements of Physiology, by Willis, p. 438, Lond., 1842.

4 Précis Elémentaire de Physiologie, 2de édit., 1825, i. 13; and Le ̧ons, &c., tom. i. p. 132.

transmission, beginning with the most powerful :--ammonia, sulphuretted hydrogen, cyanogen, carbonic acid, nitrous oxide, arseniuretted hydrogen, olefiaut gas, hydrogen, oxygen, carbonic oxide, and nitrogen."

He found that ammonia transmitted in one minute as much in volume as sulphuretted hydrogen did in two minutes and a half; cyanogen, in three minutes and a quarter; carbonic acid, in five minutes and a half; nitrous oxide, in six minutes and a half; arseniuretted hydrogen, in twenty-seven minutes and a half; olefiant gas, in twenty-eight minutes; hydrogen, in thirty-seven minutes and a half; oxygen, in one hour and fifty-three minutes; and carbonic oxide, in two hours and forty minutes. It was found, too, that up to a pressure of sixty-three inches of mercury, equal to more than the weight of two atmospheres, the penetrative action was capable of conveying the gases-the subjects of the experiment-into the short leg through the gum elastic membrane. Hence, the degree of force exerted in the penetration is considerable.

The experiments were all repeated with animal membranes, such as dried bladder and gold-beater's skin, moistened so as to resemble the natural state. The same results, and in the same order, followed as with the gum elastic. The more fresh the membrane, the more speedy and extensive was the effect; and in living animals the transmission was very rapid.

To these experiments there will be frequent occasion to refer in the course of this work.'

All these different properties of animal solids are independent of the vital properties. They continue for some time after the total extinction of life in all its phenomena, and appear to be connected either with the physical arrangement of the molecules, the chemical composition of the substance in which they reside, or with peculiar properties in the body that is made to act on the tissue. They do not, indeed, seem to be affected, until the progress of decomposition has become sensible. Hence, many of them have been termed collectively, by Haller, vis mortua.

2. FUNCTIONS OF MAN.

Having described the intimate structure of the tissues, we pass to the consideration of the functions; the character of each of which is, —that it fulfils a special and distinct office in the economy, for which it has in general an organ or instrument, or evident apparatus of organs. Physiologists have not, however, agreed on the number of distinct offices; and hence the difference, in regard to the number and classifi cation of the functions, that prevails amongst them. The oldest divi

See, connected with this subject, the ingenious papers by Dr. Robert E. Rogers, and Dr. Draper-the former in the American Journal of the Medical Sciences, May, 1836, p. 13; and the latter in the same Journal for August, 1836, p. 276; Nov. 1837, p. 122; and Aug. 1838, p. 302: and Abstract of Experiments upon the physical influences exerted by living, organic and inorganic membranes, upon chemical substances in solution passing through them by endosmose, by Joseph Jones, A. B., in the same Journal, for April, 1855, p. 555; and Experimental Investigations to ascertain the action of saline solutions of different densities upon living animals, and the reciprocal action, through dead animal membranes, of serum, water, and saline solutions; by the same, Ibid., Jan., 1856, p. 61.

sion is into the vital, natural, and animal; the vital functions including those of such importance as not to admit of interruption,-circulation, respiration, and innervation; the natural functions those that effect nutrition, digestion, absorption, and secretion; and the animal those possessed exclusively by animals,-sensation, locomotion, and voice. This classification, with more or less modification, prevails at the present day.

The character of this work will not admit of a detail of every classification which has been proposed; that of Bichat, however, has occupied so large a space in the public eye, that it cannot well be passed over. It is followed by M. Richerand,' and many modern writers. Bichat includes all the functions under two heads,-functions of nutrition, which concern the life of the individual, and functions of reproduction, which concern the life of the species. Nutrition requires, that the being shall establish relations around him to obtain the materials of which he may stand in need; and, in animals, the functions that establish such relations, are under the volition and perception of the being. Hence they are divided into two sets; those that commence or precede nutrition; have external relations; are dependent upon the will, and executed with consciousness; and those that are carried on within the body spontaneously, and without consciousness. Bichat adopted this basis; and, to the first aggregate of functions, he applied the term animal life, because it comprised those that characterize animality: the latter he termed organic life, because the functions comprised under it are common to every organized body. Animal life included sensation, motion, and expression; organic life, digestion, absorption, respiration, circulation, nutrition, secretion, &c. In animal life, Bichat recognized two series of actions, antagonistic to each other; the one proceeding from without and terminating in the brain, or passing from circumference to centre, and comprising the external senses; the other, commencing in the brain, and acting on external bodies, or proceeding from centre to circumference, and including the internal senses, locomotion, and voice. The brain, in which one series of actions terminates and the other begins, he considered the centre of animal life. organic life, he likewise recognized two series of actions: the one, proceeding from without to within, and effecting composition; the other passing from within to without, and effecting decomposition. In the former, he included digestion; absorption; respiration, by which the blood is formed; circulation, by which the blood is conveyed to different parts; and the functions of nutrition, and calorification. In the latter, that absorption by which parts are taken up from the body; the circulation, which conducts those parts or materials to the secretory or depuratory organs; and the secretions, which separate them from the economy. In this kind of life, the circulation is common to the two movements of composition and decomposition; and, as the heart is the great organ of the circulation, he considered it the centre of organic life. Lastly, as the lungs are united with animal life in the reception of air, and with organic life as the organs of sanguification, Bichat

In

1 Nouveaux Élémens de Physiologie, 13ème édit., par M. B'rard, ainé, édit. Belge, p. 42, Bruxelles, 1837; or Amer. reprint of Copland's edit. of De Lys's translation, New York, 1836.

regarded them as the bond of union between the two lives. Generation constituted the life of the species.

M. Brachet,' who gives to the sympathetic or great ganglionic nervous system a pervading influence which, it will be seen, does not properly belong to it, adopts the following classification:

METHODICAL CLASSIFICATION OF THE FUNCTIONS.

The classification, adopted in this work, is essentially that embraced by M. Magendie; and, after him, by M. Adelon, who has written one of the best systems of human physiology that we possess. The FIRST CLASS, or functions of relation or animal functions, includes those that establish our connexion with the bodies that surround us; the sensations, voluntary motions, and expressions. The SECOND CLASS, or functions of nutrition, comprises digestion, absorption, respiration, circulation, nutrition, calorification, and secretion; and the THIRD CLASS, the functions of reproduction;—generation.

In studying each of these functions, we shall first of all describe the organ or apparatus concerned in its production,-but so far only as is

Physiologie Élémentaire de l'Homme, 2de édit., i. 61. Paris et Lyon, 1855. Précis, &c., i. 32. 3 Physiologie de l'Homme, 2de édit., i. 116. Paris, 1829.