operation. He could then thread out, with some success, the trains of morbid action; and perhaps assign to each cause its proper place, in his estimate, of their agency in causing the disease. But in some cases he knows little of the mode of action, even of those agents whose influence he can perceive; and then there are some quite as important which act in entire secrecy, developing results which cannot be foreseen, and that cannot be calculated upon after they have made their appearance. Such developments are often observed in the progress of disease, and necessarily embarrasses in its treatment. They sometimes completely alter the whole character of the case. In some cases, which were in the commencement comparatively mild, a group of severe symptoms all at once start up, exciting astonishment and alarm in the mind of the practitioner.

It is sometimes impossible to detect the immediate cause of an attack of sickness, even when the transition from health to disease is apparently instantaneous. For example: A gentleman while quietly sitting in his counting-house, is attacked suddenly as if it were from a blow, with a great sense of oppression in the region of the heart, almost arresting its action, and at once prostrating his strength. No reason can be discovered why the attack should occur at this time in preference to some other. Doubtless there is some hidden cause, or combination of causes, which at the moment were called into operation, and we are unable to discover how

long the preparation for this consummation had been going on.

The Physician often finds, on making his first visit to his patient, that although he may consider his attack as a thing of to-day, there is evidence that the disease has been lurking in his system for some length of time, gradually extending its ravages, till, at length, it has made a palpable outbreak. The patient may attribute his sickness to some one cause, but there have been many causes uniting together, one after another, swelling the current which has now broken forth as a flood.

As a general rule, the longer this preparation has been going on, the more obstinate does the Physician expect the case will be, and the more difficult does he find it to obtain a definite knowledge of the nature and extent of the malady. And if he would trace every train of disease up to all its sources, both original and tributary, he would often be obliged to go back weeks, months, and, in some cases, even years. It frequently happens in attempting such an inquiry, that those facts, which in the eyes of the patient are the least material, and are often overlooked by him altogether in stating the history of his case, afford the most impartial evidence as to the origin of the disease.

These remarks apply with greater force to chronic than they do to acute disease, but, in some measure, are equally applicable to both.

Chronic cases are frequently rendered exceedingly complex and obstinate, by the course which the patient

has taken with himself, before he places himself under the care of the qualified practitioner.

He first tries domestic medication-then takes patent medicines, recommended by his neighbours, or trumpetted forth in the newspapers-then hydropathy or homoeopathy-then at last comes to a Physican, and puts himself under his care. The case which was, perhaps, sufficiently complicated in the beginning to require strict investigation, is now rendered, by this variety of practice, very intricate. The difficulty in understanding it lies in the varied effects which the different agents brought to bear on it have producedeffects which, in the retrospect, it is almost impossible to estimate with any correctness, because the Physician has only the history given him by the patient, and the appearance of his present symtoms to guide him in making up his opinions. Had he seen the case in its untouched condition, and then witnessed the operation of the different remedies, he would have been better able to arrive at satisfactory conclusions. Chronic cases need to be watched for some little time, in order to acquire a just and thorough knowledge of their character. And when they have been submitted to a series of processes at haphazard, with no intelligent eye to observe, it is no wonder they should be complicated and puzzling. In such cases the Physician is situated very much as the Chemist would be, into whose hands should be put a mixture which has been experimented upon, over and over again, by different chemists, and

those too who were ignorant and bungling; and as you would not demand of him that he should arrive at once at definite results in examining the composition of such a mixture, but would give him time to apply various tests to it, so it should not be expected of the Physician that he should understand, at once, a case which has been dabbled with by ignorant experimenters, one after another; but time must be given to watch his tests, and exhibit their real character and condition.

It must be obvious that those who go through this round of experimenting before they put themselves under the care of an educated Physician, not only lose valuable time by so doing, but generally inflict upon themselves positive harm; that frequently which, at its onset, was only a slight malady, is converted into a serious, and, too often, incurable disease.

3. I now pass on to the consideration of the third class of causes, which render medicine an uncertain science, viz.: Natural changes, arising from the tendency which exists in the system to throw off disease, appropriately called the Vis Medicatrix Nature, or curative power of nature; and, in connexion with this, the tendency to a definite limit, which is manifest in many diseases, as, for example, small-pox, measles, scarlatina and hooping-cough.

To recur to our chemical illustration-I have said that it would add vastly to the uncertainty of the results of the Chemist's experiments, if the retort into which he puts his substances to be experimented upon, could itself

act upon these substances, and thus modify their action upon each other. The body of the patient may be considered the Physician's retort, and the diseases and remedies introduced as the materials contained in it. Under this head we are to examine certain principles which reside in this retort, and which have a constant and important influence upon diseases and their remedies, modifying, sometimes manifestly sometimes secretly, their action upon each other.

I will speak first of the tendency to throw off disease, the Vis Medicatrix Naturæ. The extent to which this tendency operates is far from being properly appreciated, even by medical men, and much less by those out of the profession. The changes which it produces are certainly confounded with the effects of remedies; and this is one of the chief sources of the error which encumbers medical experience.

The reader will see, as we proceed, that boast, as doctors often will of their cures, as if they were wholly theirs, this Vis Medicatrix Nature is the chief doctor after all; and she, good, kind angel, hovering over the bed of sickness, without fee and often without acknowledgment of her services, saves the life of many a poor patient, who is near being drugged to death by some ignorant quack or over-dosing apothecary.

The following are examples of the extent of the influence of this curative principle:

If some offending substance be present in the stomach, vomiting is produced, the substance is evacuated,