1. Nature of Depletion

By this term is here meant diminution of the blood, in relation either to the whole mass, or to some one or more of its constituents. As it is these constituents of the blood to which, both through the material they furnish, and the stimulus they apply, all the vital functions owe their support, and the organs their due nutrition, the abstraction of them must necessarily occasion, in the ordinary state of the system, a depression of action and reduction of strength. It is not only, however, by diminishing the quantity of blood that depletion operates, but also by altering its quality. When a portion of the blood is abstracted, the place of the solid constituents withdrawn is rapidly supplied by the process of absorption, so that its former volume is soon restored; but, as water is absorbed in much greater proportion relatively than the solid ingredients, the blood becomes diluted, and is, therefore, less capable of performing its due office in the economy. Depletion depresses especially the force of the heart, and of the whole circulatory system. It diminishes also digestion, respiration, secretion, nutrition, calorification, and the functions of animal life. This last effect is rendered obvious when the depletion is carried far. Languor, impaired sensation, deficient emotional and intellectual energy, muscular weak-ness, even faintness, and positive syncope, result from the failure of the due influence of the blood upon the brain.

* The reader who may be familiar with my Treatise on the Practice of Medicine, in any of its editions before the fifth, will recognize, in the observations Which follow, many things which he has met with in that work. These were not introduced into the present treatise inadvertently. They essentially belong to it and could not be omitted without leaving the treatise imperfect. Their insertion here, moreover. gave me the opportunity, in revising the work on the Practice for the fifth edition of dropping in the revision the subjects here treated of, and supplying the space thus gained with new matter of a practical nature, which is ever in the course of discovery and accumulation.

But, with this general diminution of the vital powers and actions, there is one function which depletion promotes, that, namely, of absorption. 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.

Notwithstanding what has just been stated, 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; also, in the ordinary state of the blood, so far as concerns the immediate effects of depletion, and even in its ultimate effects when it is moderately used and properly guarded. But excessive depletion may act as an excitant instead of a depressing agent to certain functions, and especially those of the circulatory and nervous systems. The functions of the system generally, feeling the want of their ordinary support from the blood, make this want known to the nervous centres, which then transmit a stimulant influence to the heart, while, at the same time, they give evidence of 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. Another important rule is that, when a purely sedative effect is desired from this remedial measure, all the functions should be kept as quiescent as possible; so that, consuming little blood, they may not, from a feeling of deficiency, excite the nervous centres and through them the heart into a state of irritation. Rest should be enjoined, the food diminished, and strong mental action of emotion avoided; so that the muscles, the digestive organs, and the brain may be content with less than the ordinary supply of their essential pabulum.

2. Applications of Depletion

The therapeutic applications of depletion are obvious. It is the great remedy in plethora, and in an excess of local vascular excitement, whether that excess amount to irritation merely, or to inflammation. Sanguineous determination and active congestion, hemorrhage, morbidly increased secretion, and other derangements of function, so far as these disorders are the result of vascular irritation, are to be corrected by 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 on its influence over the absorbent process, is to the treatment of morbid effusions; the different forms of dropsy, for example, in which it is often employed with great efficacy, though requiring caution. Upon the same principle, it may be used in polysarca or morbid obesity.

3. 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.

Direct Depletion. Beyond all comparison the most efficient of the measures for direct depletion is general and local bleeding. The character of this remedy, its peculiar applications in disease, and the methods of employing it, will be fully considered in the second part of this work.

Another important mode of direct depletion, is increased secretion. 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 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 active congestion. 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.

The remedies must efficaciously employed with reference to depletion, upon this principle, are cathartics, diuretics, and diaphoretics. But all that increase secretion are occasionally useful, including expectorants, emmenagogues, sialagogues, errhines, epispasties. issues, and setons. It is upon this principle, in part, that the warm, hot, and vapour baths act usefully in certain inflammatory affections. In the application of these various remedies there is much room for discrimination; some being better adapted to one condition, others to another, and some being positively injurious where others are highly useful. This, however, is not the proper place to discuss their properties; and the reader is referred to the second part of the work. It may be proper to mention here, that such as are employed for the reduction of plethora, or inflammatory excitement, should be destitute of general stimulating properties, and that the most efficient are those which unite a sedative influence over the circulation with the power of increasing secretion. Such especially are the saline cathartics, and the antimonial diaphoretics and expectorants. A general rule applicable to all these medicines is, that, in cases of high vascular excitement, when the pulse is full and strong, and bleeding is otherwise indicated, they should be preceded by that remedy. Secretion is often checked by excess of excitement in the secreting organ, and favoured by a reduction of the excitement. Besides, medicines are not easily absorbed when the blood-vessels are full to distension. If the object be to reduce active congestion or inflammation by promoting secretion from the part or organ affected, preference should always be given, at least in the earlier stage, to those stimulants of the secretory function which are least irritant in their action. Thus, sulphate of magnesia should be preferred to gamboge, scammony, or elaterium, in the treatment of dysentery; tartar emetic or ipecacuanha to squill or seneka, in the earlier stage of bronchitis; and cream of tartar to oil of turpentine, in acute nephritis.

Indirect Depletion. This is effected by whatever prevents the usual amount of solid organic material from entering the circulation. Emetics and cathartics act in this way, by discharging the partially digested food from the alimentary canal before it has been absorbed. Still more efficacious is a temporary abstinence from food, or a reduction of its quantity and quality. But the subject of diet as a means of indirect depletion belongs to special therapeutics, and will be considered hereafter.