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blood circulates through all the textures; hence lividity, especially of those parts where the cuticle is extremely thin, as in the lips, and wherever the mucous membranes commingle with the skin; the blood gradually becomes inadequate to keep up the action of the brain and nervous system generally, as well as to stimulate the heart, and the individual gradually expires. If, again, the blood, although properly converted in the lungs, is not duly distributed to the organs, owing to the failure of the circulatory powers,either from direct or indirect causes,—the organs exhibit their correlation in the same manner, and syncope or fainting, or positive death, may be produced. Often, however, the stoppage of the action of the heart is but for a short time. Owing to some painful impression, sudden emotion, or other cause, the organ ceases to contract, either suddenly,—when the person falls down as if deprived of life,—or gradually, when the connexion of the different functions, and the order in which they fail, is manifest. Of this kind, of what the surgeon calls morbid sympathy or constitutional irritation, we have a good example in the effect of a trifling operation upon a delicate, and often upon a strong, individual. Bleeding will sometimes induce fainting, both directly, by the abstraction of fluid from the vessels, so that the brain may cease to act; and indirectly, when the quantity removed cannot be presumed to have exerted any influence. Some, indeed, will faint from the slightest puncture and loss of blood, or even from the sight of that fluid. In these last cases, if the syncope come on gradually, a feeling of great anxiety and oppression, occasionally of vacuity, exists in the epigastric region; the perceptions become confused, the sight obscured, tinnitus aurium and dizziness supervene, the respiration is embarrassed, the face pale, the extremities cold, and the different parts of the body are covered with a cold, clammy sweat, until ultimately loss of sensation and motion supervenes, and the individual is temporarily dead; from which state, however, he soon recovers in the generality of cases, provided he is kept in the recumbent posture, so that the blood may readily pass to the brain. On other occasions, the heart will not cease its pulsations, but will continue to send blood, in undue quantity, to the brain, so that all the above symptoms may ensue, except the temporary privation of vitality. In consequence of the severe pain induced by a displacement of two of the bones of the wrist, by a fall from a carriage, the author remained a considerable time deprived of sight, and at the same time suffering from great anxiety, yet the action of the heart never ceased, so as to induce complete syncope.

The third vital function,—that of innervation,—when suspended or diminished, draws on a train of pathological phenomena, in the order described under the head of death; suspending respiration and circulation suddenly, if the cause applied be sufficient; more gradually, and with the symptoms characterizing apoplexy or compres

sion of the brain, if the cause act in a minor degree. All the three vital functions are consequently correlative, and so intimately associated, that if a malign influence act upon one, the effect is speedily extended to the other.

Owing to the necessity for the blood possessing certain attributes, the most important of which are obtained by its circulation through the lungs, we can readily understand, that if the functions. of nutrition are not properly exerted, the composition of that fluid may be imperfect, and disorder take place in various parts of the frame from this cause. Thus, if digestion or the formation of chyle be not properly executed, the blood is pot duly renovated, and may be so far impoverished, that the play of the functions are interfered with. We have elsewhere shown, that if omnivorous man be restricted to one kind of diet he will fall off, and become scorbutic, and that the affection will be removed by allowing him diet of another kind;—vegetables, if animal food have induced it, and vice versa. Enlarged mesenteric glands, consequent, or not, on inflammation of the mucous membrane of the intestine, and the latter affection itself, are cases which may interfere with chylosis, and consequently with the constitution of the blood. In like manner, if nutrition and the various secretions are not duly performed in the tissue of the organs, and especially if the two great depurations,—the urinary and cutaneous,—be obstructed, the blood may suffer, and although the due changes from venous to arterial may be effected in the lungs, its character may not be such as to adapt it for the healthy execution of the various functions.

The humorists assigned too much importance to the condition of the humours in the production of disease; the solidists, on the other hand, have denied it almost all agency. The medium between these exclusionists is probably the nearest to nature. The solitary fact of black blood being unfit to maintain the vitality of any organ sufficiently exhibits its lethiferous influence. How the arterial blood exerts its agency, independently of its action as a fluid of nutrition, is beyond our knowledge. It appears to exert a necessary action of stimulation, but in what manner, or on what element, we know not: probably, however, its chief influence may be on the nervous tissue, as the privation of arterial blood occasions the immediate cessation of the action of the brain.

The second of the essential elements to the continued existence of the frame and of every part of it is the nervous influence. In the higher classes of animals, this is dispensed from three great centres, the encephalon, the spinal marrow, and the great sympathetic. The presidency, however, may be fairly assigned, in man and in the higher animals, to the first of these. If it fails, death soon becomes general. This, however, is liable to great variation in different animals, and likewise in different functions. In man, if the nervous supply be cut off from any part, the part dies.

Physical integrity, continuity, and a due supply of arterial blood, are necessary to the proper exercise of the nervous power. In a former part of this work, the wonderful resistance to death, which characterizes the amphibia, and the comparative independence of each portion of the body, in some of the lower orders of animals, were pointed out. The polypus can be divided into numerous pieces, yet each may constitute of itself a distinct animal. The snail, after decapitation, reproduces the head; and a similar reparatory power is possessed by other animals. We have elsewhere seen, that volition is seated lower in the inferior than in the superior orders of animals; and that in man it is chiefly,—some say wholly,—restricted to the encephalon.

It appears, likewise, that the dependence of the rest of the nervous system on the great nervous centres is less in young than in old animals. Edwards regarded the new-born child as resembling, in many respects, the cold-blooded animal, and Redi, Rolando, and Flourens, and Legallois found that the tenacity of life, after decapitation, was much greater the nearer to birth.

The functions also differ with regard to their dependence upon the encephalon. Disease may attack the animal functions and suspend them for a considerable length of time,—as in apoplexy, -before the organic functions are interfered with. This is a topic, however, which will be discussed under the head of DEATH.

We may conclude, then, that "life," to use the language of a gifted preceptor of the author,—M. Beclard,—" consists essentially in the reciprocal action of the circulation of the blood and innervation; death always following the cessation of such reciprocal action." But this conclusion is applicable only to animals; although both circulation and innervation are admitted in the vegetable by some physiologists. Legallois, from his experiments deduced the unwarrantable inference, that "life is owing to an impression made by arterial blood on the brain and spinal marrow, or to the principle which results from this impression;"—a definition which would exclude the numerous animals of the lower classes, as well as vegetables, which are deficient in both brain and spinal marrow.

The conclusion of Beclard is the limit to our knowledge on this subject. Yet some have endeavoured to discover which of the two functions,—circulation or innervation,—holds the other in domination. They, who consider the nervous substance to be first formed in the foetus, ascribe the supremacy to it; whilst the believers in the earlier formation of the sanguiferous system look upon it as the prime agent. We know no more than that both

"Maintain

With the mysterious mind and breathing mould
A co-existence and community."

In every important function of the body we find this correlation

or catenation of organs existing; all working to one end, and all requisite for its perfect accomplishment. How many organs, for example, are required to co-operate in the elevated function of sensibility! The encephalon, the seat of thought, receives by the external senses the various impressions which act upon them from without, and, by the internal sensations, such as arise in the economy and are generally the indexes of the physical necessities or wants. The intellectual and affective faculties enable us to appreciate the various objects that occasion our sensations, and indicate our social and moral wants: under their direction volition is sent out, which acts upon the various muscles, and produces such movements as may be required for carrying into effect the suggestions of the mind. Between all these acts there is the closest catenation.

In like manner, we observe the correlation between the animal, and the nutritive, and reproductive functions. The internal sation of hunger suggests to the mind the necessity for a supply of aliment; the external senses are called into action to discover the proper aliment; when discovered, it is laid hold of by muscular movements under the direction of volition, is subjected to various voluntary processes in the mouth, and then passed on, by a mixed voluntary and involuntary action, into the stomach. In like manner, the desire for sexual intercourse may be excited in the mind through the organs of vision or touch; the organs of generation are aroused to action, and the union of the sexes is accomplished by the exertion of muscles thrown into contraction by volition. The same catenation is exhibited after a fecundating copulation: menstruation, which was previously performed with regularity, is now arrested; the breasts become developed; milk is formed in them, and whilst the female suckles her child, unless the period is unusually protracted, the nonexistence of the menstrual function continues.

Almost all the phenomena of disease are connected with this correlation of functions. Derangement takes place in one organ or structure of the body, and speedily all those that are correlated with it participate in the disorder. Hence, in part, arises the combination of disordered nervous, circulatory and secretory function, which characterizes general fever; and the various associated morbid actions that constitute disease in general.

There is another kind of connexion which distinguishes the animal body from a piece of ordinary mechanism yet more than those we have considered. In this, owing to an impression made upon one organ, distant organs become affected, without our being able to refer the transmission to mechanical agency, or to the association of functions which we have just described. This kind of association is called sympathy. A particle of snuff or other irritating substance, impinging on the Schneiderian membrane, produces itching there, followed by a powerful action of the whole

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respiratory apparatus, established for its removal. The sneezing, thus induced, is not caused by the transmission of the irritation through the intermediate organs to the respiratory muscles; nor can we explain it by the mechanical or functional connexions of organs. It is produced by this third mode of correlation :—in other words, it is a case of sympathy.

Again, a small wound in the foot will produce locked jaw, without our being able to discover, or to imagine, any greater connexion between the foot and the jaw than there is between the foot and other organs of the body. We say that it is caused by sympathy existing between these organs, and, so long as we use the term to signify the unknown cause of these connexions, it is well. It must be understood, however, that we attach no definite idea to the term; that it is only employed to express our ignorance of the agent or its mode of action; precisely as we apply the epithet vital to a process which we are incapable of explaining by any physical facts or arguments.

Of sympathetic connexions, we have numerous examples in the body; at times, inservient to accomplishing a particular function; but generally consisting of modifications of function produced by the action of a distant organ. Of the sympathetic connexion between the parts of the same organ, for the execution of a function proper to the organ, we have an example in that between the iris and the retina; the former will contract or dilate according to the degree of stimulation exerted by the light on the latter; and the effect is greater when the light is thrown on the retina than when thrown on the iris itself.

A similar kind of sympathy exists between the state of the mammæ and that of the uterus, during pregnancy; although this has been frequently referred to ordinary functional correlation or synergy; but the connexion is sufficiently obscure to entitle it to be placed under this division.

Sympathies of continuity are such as occur between various parts of membranes that are continuous. For example, the slightest taste or smell of a nauseous substance will bring on an effort to vomit,--the whole of the first passages being unfavourably disposed for its reception. In disease we have many examples of this kind of sympathy. During dentition the child is subject to various gastric and intestinal affections. If a source of irritation exist in any part of the intestinal or other mucous membrane, no uneasy sensa tion may be experienced at the seat of irritation, yet it may be felt at the commencement of the membrane or where it commingles with the skin:—thus, itching at the nose may indicate irritation of the digestive mucous membrane;—itching or pain of the glans penis, stone in the bladder, &c. These facts prove that in disease a sympathetic bond unites the parts concerned, and such is probably the case in health also. We have the same thing proved in the effect produced on the action of glands by irritating the orifices of their excretory ducts. The presence of food in the

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