These are medicines which have the special property of promoting the menstrual discharge. Difference of opinion has existed in regard to the nature of this evacuation, whether it is to be considered as a secretion or hemorrhage. That it is not the result of secretion, in the sense in which some modern physiologists regard this function, as performed, namely, through the agency of cells, is very obvious; for, examined by the microscope, it is found to contain the red corpuscles of the blood unchanged, and these could hardly have entered into the interior of a cell with a perfect integrity of their envelope.

But, though not a secretion, in this sense of the term, it cannot, I think, be considered as a simple hemorrhage. The liquid eliminated differs from blood in some material points, the most prominent of which is its want of coagulability. it is urged, in reply to this objection, that the property of coagulation is lost in consequence of the slowness with which the blood oozes out from the vessels, and of its intimate mixture with the mucus. But the menstrual fluid often escapes in considerable quantities, still characterized by its want of coagulability; and it is only when the normal discharge is replaced by a true hemorrhage, that the fibrin exhibits its coagulating property. There are generally also differences in colour and odour, which indicate an absence of perfect identity with blood. Besides, the discharge is frequently preceded and followed by the escape of a whitish or colourless liquid; and there seems to be a gradual passage from one of these kinds of discharge to the other; and sometimes, indeed, an intermediate condition between the two. The menstrual fluid, therefore, differs from pure blood. it is undoubtedly separated from the circulating mass, and probably undergoes some modification in the act of separation. The term secretion, in its widest sense, might apply to a liquid of this kind. The menses, therefore, in this view of the subject, may be looked on as a secretion.

That it is not a mere hemorrhage would seem also to be inferrible from the following considerations; that it occurs at a regular period, and in obedience to certain fixed laws; that it has an important influence upon conception; that, from its regular periodicity, it is probably under the control of the organic nervous centres; and that it does not depend, as hemorrhage generally does, either on a simple general or local plethora, a morbid state of the blood, or a relaxed and debilitated state of the vessels. The system may be in every stage of plethora, from the lowest to the highest, and the uterus in every grade of active congestion up to inflammation, and yet the menstrual flux shall not occur, except at the appointed time. it can scarcely be doubted that, under the special laws governing the female economy, and operating probably through the organic nervous centres, the vessels of the uterus assume at certain periods a special condition, in which a certain amount of blood is thrown off, somewhat modified in its obvious characters, and with an important purpose. it is then, strictly speaking, a special function that is performed, in the act of menstruation.

Some deny that there are any emmenagogues, that is, medicines calculated to promote menstruation by a special influence. But why should there not be such medicines ? The process has been shown to be an important and peculiar function; and what is there in it, so different from other functions, that it cannot have its special stimulants? From analogy we should rationally infer that it would probably have such stimulants; and the question is then one of mere experience and observation, whether it has or not. Now assuredly there are medicines, under the influence of which the menses, long suppressed, are very frequently restored, and when existing are increased; and some have been found to have much greater influence than others, independently of any difference in mere stimulant power over the uterine circulation. That they operate less uniformly than some other secretory stimulants, and often fail to act at all, probably depends on the fact, that, in order to the performance of the function, there must be a special state of the uterus induced, and this can be induced normally only at particular periods. Unless in this condition of the womb, emmenagogues cannot act as such. They may produce local plethora of the organ and consequent hemorrhage, but they cannot bring on the proper menstrual flux. They may, however, aid nature in inducing the peculiar condition referred to, and, when it exists, may bring on the exercise of the function to which nature herself may be inadequate.

Except in its periodicity, menstruation obeys the same general laws with the other secretory functions, and the influences which promote it operate upon the same general principles.

Not unfrequently the function is suppressed in consequence of a vascular irritation or active congestion of the womb, with or without general plethora and excitement, in obedience to the general law, that a certain excess of excitement in an organ diminishes or suspends its function. Under these circumstances, whatever diminishes the excitement down to the point at which it is calculated to increase function, may bring on the discharge; and bleeding, the saline cathartics, the antimonials and other refrigerants, the free use of warm diluent liquids, the warm bath, etc., may act as emmenagogues, if not carried so far as to substitute a state of depression for that of excitation previously existing.

Again, like all other functions, menstruation is defective or suppressed through a want of sufficient energy, either of the uterus itself, or the nervous centres which govern it. The organ is in a state of torpor, inertness, or debility. This condition may be entirely local; in which case medicines calculated specially to stimulate the uterus itself, or its nervous centres, operate as emmenagogues. Or it may depend on a debilitated state of the system generally, and especially upon an impoverished condition of the blood, in which that fluid is incapable of affording the necessary healthy stimulus to the function. In such a case, it is obvious that the remedies, calculated to bring about a return of the function, are those which are fitted to give energy to the system at large; as tonics, a nutritious diet, and, in the anemic state of the blood, the chalybeates especially.

When, so far as can be discovered, there is no excitation or depression of the system or the organ, and yet the function is insufficiently performed, or not at all, the application of a gentle stimulation to the uterus, without anything specific in its character, will often induce a return of the menses. Purges which irritate the lower portion of the bowels, and stimulating diuretics which produce the same effect on the urinary passages, may act on the uterus and its appendages by a kind of contiguous sympathy, and thus stimulate its function. Stimulating injections into the vagina, as, for example, of solution of ammonia sufficiently diluted, will have the same effect. The hot hip-bath operates in a similar manner. But perhaps no direct excitant agency is equal to that of electricity, which has frequently a powerful effect in restoring the menses. (See i. 539.) Active and vigorous exercise often has the same effect. Even a fixed attention of the mind upon the function will sometimes, it is asserted, bring it into operation.

The proper or special emmenagogues probably operate by absorption into the circulation, and a direct action on the uterus, the ovaries, or the nervous centres, or all three together, so as to induce the menstrual tendency, at the same time that they directly excite the uterine vessels.

Whatever may be the methods employed, they are most effectual when brought to bear upon the system at the regular period for the menstrual effort, at which time very slight causes are often sufficient to bring on the discharge. When pain, or a sense of weight in the loins, flushed face, headache, and various abnormal sensations, give evidence that the period is present, it will often happen that warm pediluvia, the warm bath, or warm gently stimulating and diaphoretic teas, taken at bedtime, will restore the function.

In considering the several medicines which have claims to be treated vol. II.-45 as emmenagogue, we find that they may be arranged in three or four subdivisions, based in part upon the possession of other than pure em. menagogue properties. Thus, we have tonics, purgatives, and stimulating diuretics, which appear to possess special influence over this function also; while certain medicines, without particular tendency to other functions, are peculiarly and prominently emmenagogue. Under these divisions, I shall consider the several medicines which seem to me to merit a place in this class.