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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 transmission, beginning with the most powerful:-ammonia, sulphuretted hydrogen, cyanogen, carbonic acid, nitrous oxide, arseniuretted hydrogen, olefiant gas, hydrogen, oxygen, carbonic oxide, and nitro

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.'

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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;

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 classification of the functions, that prevails amongst them. The oldest division 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

and the latter in the same Journal for August, 1836, p. 276; Nov. 1837, p. 122; and Aug. 1838, p. 302.

* Nouveaux Elémens de Physiologie, 13ème édit., par M. Bérard, ainé, édit. Belge, p. 42, Bruxelles, 1837; or Amer. reprint of Copland's edit. of De Lys's translation, New York,

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. In 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 depuratory organs; and the secretions, which separate them from the economy. In this kind of life, the circulation is cominon 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 regarded them as the bond of union between the two lives. Generation constituted the life of the species.

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.

TABLE OF FUNCTIONS.

1. Sensation.
I. Animal or of Relation. 2. Muscular Motion.

3. Expression or Language. I. Functions that relate to

4. Digestion.

5. Absorption. the preservation of the indie vidual.

6. Respiration.
II. Nutritive.

7. Circulation.
8. Nutrition.
9. Calorification.

10. Secretion.
II. Functions that relate to
III. Reproductive.

11. Generation. the preservation of the species.

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 necessary in a physiological point of view; and shall next detail what has been called the mechanism of the function, or the mode in which it is effected. In many cases, it will happen, that some external agent Précis, &c., i. 32.

· Physiologie de l'Homme, 2de élit., i. 116. Paris, 1829.

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is concerned, -as light in vision; sound in audition; odours in olfaction ; tastes in gustation. The properties of these agents will, in all instances, be detailed in a brief manner.

The difficulty of observing actions, that are carried on by the very molecules of which the organs are composed, has given rise to many hypothetical speculations, some of which are sufficiently ingenious; others too fanciful to be indulged for a moment; and, as might be expected, the number of these fantasies generally bears a direct proportion to the difficulty and obscurity of the subject. It will not be proper to pass over the most prominent of these, but they will not be dwelt upon; whilst the results of direct observation and experiment will be fully detailed; and where differences exist amongst observers, such differences will be reconciled, where practicable.

The functions, executed by different organs of the body, can be deduced by direct observation; although the minute and molecular ac by which they are accomplished in the very tissue of the organ, may not admit of detection. We see blood proceeding to the liver, and the vessels that convey it ramifying in the texture of that viscus, and becoming so minute as to escape detection even when the eye is aided by a powerful microscope. We find, again, other canals in the organ becoming perceptible, gradually augmenting in size, and ultimately terminating in a larger duct, which opens into the small intestine. If we examine each of these orders of vessels in their most minute appreciable ramifications, we discover, in the one, always blood; and, in the other, always a very different fluid, -bile. We are hence led to the conclusion, that in the intimate tissue of the liver, and in some part communicating directly or indirectly with both these orders of vessels, bile is separated from the blood; or that the liver is the organ of the biliary secretion. On the other hand, functions exist, which cannot be so demonstratively referred to a special organ. We have every reason for believing, that the brain is the exclusive organ of the mental and moral manifestations; but, as few opportunities occur for seeing it in action; and as the operation is too molecular to admit of direct observation when we do see it, we are compelled to connect the organ and function by a process of reasoning only; yet, we shall find, that the results at which we arrive in this manner are often by no means the least satisfactory.

The forces which preside over the various functions are either general,—that is, physical or chemical; or special,—that is, organic or vital. Some of the organs afford us examples of purely physical instruments. We have in the eye, an eye-glass of admirable construction; in the organ of voice, an instrument of music; in the ear, one of acoustics : the circulation is carried on through an ingenious hydraulic apparatus ; and station and progression involve various laws of mechanics. In many of the functions, again, we have examples of chemical agency, whilst all in which innervation is concerned are incapable of being explained on any physical or chemical principle; and we are constrained to esteem them vitai.

BOOK I.

ANIMAL FUNCTIONS OR FUNCTIONS OF RELATION.

The functions of relation consist, first, of sensibility, and, secondly, of muscular motion, including expression or language. They are all subject to intermission, constituting sleep; a condition which has, consequently, by many physiologists, been investigated under this class; but as the functions of reproduction are influenced by the same condition, the consideration of sleep will be deferred until the third class of functions has received attention.

CHAPTER I.

SENSIBILITY.

SENSIBILITY is the function by which an animal experiences feeling, or has the perception of an impression. In its general acceptation, it means the property possessed by living parts of receiving impressions, whether the being exercising the property has consciousness of it or not. To the first of these cases-in which there is consciousnessBichat gave the epithet animal; to the second, organic; the latter being common to animals and vegetables, and presiding over the organic functions of nutrition, absorption, exhalation, secretion, &c.; the former existing only in animals, and presiding over the sensations, internal as well as external. Animal sensibility will be considered here. It would be well, indeed, to restrict the term sensibility to cases involving consciousness.

Pursuing the plan already laid down, the study of this interesting and elevated function will be commenced, by pointing out, as far as may be necessary, the apparatus that effects it, the nervous system.

1. NERVOUS SYSTEM. Under the name nervous system, anatomists include all those organs that are composed of nervous or pulpy tissue-neurine. In man, it is constituted of three portions: first, of what has been called the cerebrospinal axis, a central part having the form of a long cord, expanded at its superior extremity, and contained within the cavities of the cranium and spine; secondly, of cords, called nerves, in number thirty-nine pairs, according to some,—forty-two, according to others,-passing laterally between the cerebro-spinal axis and every part of the body; and, lastly, of a nervous cord, situate on each side of the spine, from the head to the pelvis, forming ganglia opposite each vertebral foramen, and called the great sympathetic.

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