8. Coincident influences often greatly modify the morbid results of particular causes. Of these, perhaps, the most important are the miasmatic influence, and that of epidemics. Without attending to these, the practitioner must be liable to the most fatal blunders. It is well known that all the diseases of miasmatic regions assume a character more or less analogous to that of the peculiar fevers by which they are infested. Fevers arising from other causes, and even the ordinary phlegmasiæ, occurring in the autumn and winter, exhibit generally the remittent aspect of the proper miasmatic fever, and, like it, require less depletion than in other situations, and often yield most happily to quinia. Epidemics are notorious for their quality of imparting something of their own nature to all other co-existing diseases. Now sometimes the epidemic influence conduces to a sthenic or vigorous state of system, sometimes to an asthenic, feeble, or typhoid condition. In the former case, diseases ordinarily of a feeble character assume a degree of energy and elevation which requires depletion; in the latter, inflammatory complaints, which usually yield most readily to copious bleeding, sometimes become so prostrate as to forbid evacuation, and even to require the support of active stimulation. This latter effect was frequently witnessed in this country, during the prevalence of our great typhous epidemic.

9. The pointings of nature should be watched for, and regarded in the treatment of diseases, even though they may be opposed to the deductions of our reason, and the whole previous course of our experience. Now and then, in the progress of a disease, the patient expresses a wish for some article of food or drink, some medicine, or some change in other respects in his management, which seems to the physician altogether improper. As similar wishes are often the mere result of the restlessness and caprice of disease, it is of course very properly denied by the physician. But if the same wish is repeated time after time, resisting alike the authority of the physician, and the common sense of the patient himself, it acquires an altogether different value. It may now be looked upon as probably a real want of the system, an indication presented by nature, which ought to be indulged. At first, however, it should be gratified cautiously, and in such a manner that little harm could result if it should happen to be a mistake. Should apparent good result from the first careful trial, a greater latitude may be allowed; and the practitioner will often be gratified at witnessing a rapid recovery, dating from the moment of his judicious surrender of his own judgment to this imperious call of the system.

10. It is a good general rule of practice, whatever may be the particular disease under treatment, to attend to the state of the functions, and to correct any disorder in them, even though not directly connected with the disease. The bowels, especially, should be kept regular, and fecal accumulation sedulously guarded against. The secretions of the liver, skin, and kidneys, should be preserved as nearly as possible in a healthy state. Irregularities in the circulation, the diffusion of temperature, and the nervous actions, should also receive attention. As it is not always possible to determine how far diseases are mutually dependent, we may thus occasionally cut off, unknowingly, one of the roots of the principal affection, and render its cure comparatively easy. 11. There are various effects of disease which require treatment, without reference to any morbid condition of the vital actions. Such are certain liquid accumulations, as in different forms of dropsy; organized solid products of deranged secretion, as in the swelling and hardness which inflammation often leaves behind it; and various solid deposits from the fluid secretions, as urinary and biliary calculi. These, however, as they constitute special diseases, and offer special indications, do not call for particular consideration in this place.

SECTION II.

GENERAL THERAPEUTIC PROCESSES.

These may be included under the heads of 1. depletion; 2. repletion; 3. dilution; 4. stimulation; 5. sedation; 6. revulsion; 7. supersession; 8. alteration; 9. elimination; 10. chemical action; and 11. mechanical action.

I. Depletion.-By this term it is intended to express a diminution of the blood, in relation either to the whole mass, or to some one or more of its solid constituents. When a portion of the blood is abstracted, the quality as well as the quantity of that fluid is altered. One of the consequences of diminution in the contents of the blood-vessels is increased absorption; and, as water is absorbed in much greater proportion than the solid principles, the consequence is that the blood becomes diluted. It is, therefore, less stimulant, and less capable of affording the due support to the functions, almost all of which are directly dependent upon it. Depletion consequently tends, by a reduction both in the quantity and quality of the blood, to diminish the vital actions. It depresses especially the force of the heart, and of the whole circulatory system. It diminishes also digestion, respiration, nutrition, secretion, calorification, and the functions of animal life. This last effect is rendered obvious, when depletion is carried to any considerable extent. Languor, impaired sensation, deficient emotional and intellectual energy, muscular weakness, even faintness, and positive syncope, result from the failure of the due influences of the blood upon the brain. But there is one function, that of absorption, which appears to be promoted. To supply the loss of blood, the liquids and solid tissues of the body are taken up with more than the usual rapidity, and water is copiously absorbed from the contents of the alimentary canal, and perhaps also from the external air.

APPLICATIONS.-The therapeutical applications of depletion are obvious. It is the great remedy in plethora, and in excess of vascular excitement, whether that excess amount to irritation merely, or to inflammation. Sanguineous determination and congestion, hemorrhage, morbidly increased secretion, and other derangements of function, so far as these disorders are results of irritation, are to be combatted by means of it. In the treatment of inflammation it is invaluable; not only lessening the force with which the blood is driven into the inflamed part, but impairing those qualities of the vital fluid which most powerfully support that morbid process.

Another application of depletion, dependent upon its influence over the absorbent process, is in the treatment of morbid effusions, the different forms of dropsy, for example, in which it is often employed with great efficacy, though requiring caution. (See Dropsy.) Upon the same principle, it may be used in polysarca or morbid obesity.

From what has been stated in a former place (see pages 66 and 67), the reader is prepared to understand that depletion is not always purely sedative; and this is a very important therapeutical fact. The general rule may be considered as holding true, whenever the blood is in excess, as regards its animalized or vital constituents. Under these circumstances, therefore, the remedy may be employed without hesitation, if indicated by any obvious derangement. The same is true also, even in the ordinary state of the blood, as regards the immediate effects of depletion, and even its ultimate effects, when moderately used and properly guarded. But copious depletion, when mistakenly used, may act as an excitant instead of a depressing agent to certain functions, and

especially those of the heart and nervous system. The functions of the system generally, feeling the want of their wonted support, make this want sensible to the nervous centres, which then transmit a stimulant impression to the heart, while, at the same time, they make known their own disturbance by various irregular nervous phenomena. Under no circumstances, is the heart thrown into more violent commotion than, sometimes, through an impoverished condition of the blood. Depletion, therefore, especially the more direct and powerful kinds of it, should be employed with reserve in anemic states of the circulation, even though strongly indicated by other considerations.

MEANS OF DEPLETION.-Depletion may be effected either directly, by taking blood or promoting secretion, or indirectly, by diminishing the supplies through which the natural losses of that fluid are repaired. Beyond all comparison, the most efficient of these measures is the immediate abstraction of blood from the vessels, either quickly through one large opening in a vein or artery, or by means which withdraw it slowly and through numerous small openings. The former is called general, the latter local bleeding.

General Bleeding.-When blood is taken directly from an artery, the process is called arteriotomy; when from a vein, venesection. In the former, the temporal artery is almost always selected; but the operation is scarcely ever employed except in violent diseases of the brain, and is probably never necessary even then. Venesection is almost universally preferred. This is usually performed in the arm, at the bend of the elbow; and, where a vein sufficiently large can be found in this position, there is seldom any necessity for having recourse to another.

The general effects of bleeding are those already detailed as the result of depletion. Its peculiar effect is, at first, merely to diminish the quantity of the circulating mass by the amount abstracted, afterwards to lessen especially the proportion of red corpuscles. It is true that the whole amount of solid ingredients in relation to the liquid is diminished; but the albumen and fibrin suffer less than the coloured constituent, probably because they are more readily supplied from the tissues and food, through the processes of digestion and absorption. Indeed, in inflammation, the proportion of fibrin, according to Andral, even increases up to a certain period, notwithstanding the loss of blood. But, as the red corpuscles are probably the most stimulating ingredient, the effect of the bleeding is greatly to diminish the excitant properties of the blood, even in inflammation.

The loss of a sufficient quantity of blood will always produce syncope; but the amount requisite for this effect varies greatly in different individuals, and in different diseases. In plethora and inflammation, more is required than in health; in anæmia and asthenia, or typhous affections, less; the difference probably depending upon the more or less stimulant quality of the blood. The nature also of the tissue inflamed has some influence upon the tolerance of the loss of blood. It is well known that posture has great effect. When lying down, an individual will bear a greater loss than when sitting, and in this position than when standing. This is owing partly to the effect of gravitation, favouring or otherwise the pressure upon the brain; partly, to the greater amount of blood required to support the increased muscular action, in the two latter postures. According to Dr. Marshall Hall, the mean loss of blood requisite to produce the symptoms of commencing syncope, in the sitting or erect posture, is in health 15 ounces, in congestion of the brain from 40 to 50 ounces, in inflammation of the serous, synovial, or fibrous membranes, from 30 to 40 ounces, in parenchymatous inflammations 30 ounces, in mucous and cutaneous inflammations 16 ounces; while, in eruptive fevers, it is only 12 to 14 ounces, in delirium tremens 10 to 12, in accidents before

inflammation has taken place, 8 to 10; and in chlorosis 8. But these are mere approximations; and the numbers are liable to very great diversities. Much depends upon the rapidity with which the blood is drawn. When it flows in a full stream, through a large orifice, faintness is induced by a much smaller quantity than when it is taken very slowly, or by small and repeated portions.

The quantity of blood to be drawn, in any particular case, must vary not only with the tolerance of the individual or the disease, but with the particular object to be accomplished. When strong determinations of blood to the brain, or the lungs, threaten death from cerebral or pulmonary apoplexy; or when violent inflammatory spasm puts life in immediate danger, as in some cases of laryngitis; or when inflammation of extraordinary violence attacks some vital organ, the bleeding may often proceed till symptoms of approaching syncope appear. But, in ordinary cases of vascular irritation or inflammation, this is seldom necessary. It is usually sufficient, in these cases, to produce a sensible diminution in the force of the pulse; and it is safer to bleed a second time, if requisite, than to abstract too much at once. Bleeding to absolute syncope, in fixed affections, is injurious, independently of the mere quantity of blood lost. According to principles sufficiently developed in previous parts of this work, the repose of all the organs, during the state of fainting, increases their excitability; and, when action is restored, it is very apt to run into extremes. Hence, the pulse becomes, under such circumstances, not unfrequently more excited and tumultuous, though less tense, than before the bleeding.

If

The mode of taking blood varies with the indication to be fulfilled. syncope or an approach to it be desirable, the orifice should be large; and if it be wished, as may not unfrequently happen, to produce the effect with as little loss of blood as possible, the patient should be bled sitting or standing. If, on the contrary, it is deemed important to take away a large amount of blood, without inducing syncope, the patient should be in a lying position, the orifice should be rather small, and the current occasionally stopped for a time by the finger, so as to allow the heart and brain to accommodate themselves to the diminished tension of their vessels.

In doubtful cases, in which the propriety of bleeding may be uncertain, but in which the strength of inducement may be somewhat in its favour, the patient should be placed, if possible, in the sitting posture, or even upon his feet, and the operation should cease as soon as any signs of faintness appear.

Local Bleeding. This is usually effected by cupping or leeches. The former is generally preferable, when the surface from which it is desirable to abstract blood is extensive, and not tender under pressure. It also adds the influence of revulsion, through the inflammation excited by the wounds, to that of depletion. Leeches are preferable when the part is tender, when the surface is irregular or of very loose texture, and when it is desirable to concentrate the application within a very small space. They should always be used, preferably, in the cases of infants. In this work, when the number of leeches is mentioned, reference is always had to those of American growth, unless the fact is otherwise expressly stated. European leeches draw much more blood than the American, and, if employed in the number directed for the latter, might produce dangerous exhaustion. The American have the advantages of being more readily procured, more easily regulated in relation to the quantity of blood they draw, and less apt to be followed by obstinate hemorrhage.

Local bleeding is often adequate, of itself, to the cure of inflammation, when this is moderate, and not attended with general excitement. It may also be advantageously employed in those doubtful cases, in which, while an indication for the loss of blood is offered by the existence of inflammation, the general

strength may be inadequate to support bleeding from the arm. But, most frequently, it is employed only as an adjuvant to general bleeding. When inflammation is accompanied with fever and a sthenic state of system, cups or leeches, employed in any ordinary measure, are quite inadequate. The capillaries are, in such cases, rapidly refilled through the vis a tergo, and little impression is made on the disease. But, after excitement has been sufficiently subdued by the lancet, or general bleeding has been carried as far as may be deemed consistent with the strength of the patient, local bleeding may often be resorted to, with great advantage, to complete the cure. In infants, however, leeches will frequently answer all the purposes of bleeding from the arm.

Local bleeding has the advantage, over general, of producing a greater effect upon the local disease, with less loss of blood. In order that it may act most effectively, the blood should be taken from the immediate vicinity of the inflamed part, but not, as a general rule, from the inflamed vessels themselves; as the irritation of the wound sometimes increases the disease which the depletion was intended to relieve. The remedy is often applied, with great advantage, in cases of internal inflammation, to the outer surface directly over the part affected. Its efficacy, in such cases, can be readily understood, when the part inflamed has a direct vascular communication with the exterior surface, as in costal pleurisy. The blood may be conceived to proceed immediately from the inflamed vessels. But the remedy proves scarcely less beneficial in the affections of organs which have no such direct connexion, as in mucous gastritis and in bronchitis. Its mode of operating, under these circumstances, is not so easily explained. Some have ascribed the result to derivation; but they do not inform us why the same amount of blood, drawn in another place, would not answer the same purpose; why, for example, it must be taken from the epigastrium in mucous gastritis, and not from between the shoulders, from the breast, or some other part quite as closely connected by vessels as the epigastrium with the mucous membrane of the stomach. I know no better explanation than that which supposes a sympathy to exist between the internal organs and the corresponding portion of the outer surface, by which an impression made on the latter is propagated to the former, through some common nervous centre. This, however, is purely hypothetical.

The quantity of blood which it may be proper to take by cups or leeches has no precise limits. It may not be more than an ounce or two, or it may amount to ten or twelve ounces. Generally, from two to six or eight ounces will be sufficient. Each American leech may be estimated to draw a fluidrachm, or a little more.

Increased Secretion.-This is another very useful mode of depletion. It not only unloads the circulation in general, but, in some cases, has the advantage over bleeding, of directly depleting from the diseased vessels themselves, and thus of imitating a very frequent process of nature in the relief of irritation and inflammation. Thus, cathartics relieve mucous enteritis, expectorants bronchitis, and diuretics nephritis. It is not merely the watery parts of the blood that are thus evacuated, but its animalized constituents also, though the red corpuscles seldom pass. Upon the whole, this mode of depletion is much less efficacious than bleeding, in the relief of plethora and vascular excitement. But, for the purpose of promoting the absorption of effused fluids, it is even more efficacious; as a much larger amount of liquid may be safely abstracted from the blood-vessels by increased secretion than by bleeding, and consequently a greater amount of absorption produced. Another advantage which it possesses is the elimination of noxious matters from the blood-vessels; and there is reason to believe that much good is often effected in this way.

The remedies most efficaciously employed with reference to depletion, upon