If, then, there be so much ground for difference of opinion in regard to the nature of the causes of disease, and their mode of operation, where the results are of so definite a character, as we see in the disorders to which I have alluded; much more is this the case with those diseases, which, with their Protean shapes, make up a large proportion of the maladies that call for the daily attention of the physician. _These_ do not commonly spring from one cause, but from many causes concurring together, some of which may be ascertained, while others are only suspected, or are wholly concealed from the most scrutinizing investigation. Under these circumstances, the physician has a difficult task to discover the actual condition of the patient. It would be a comparatively easy one, if he knew what all the agents were that had combined to produce the disease, even though they were numerous and complicated in their operation. He could then thread out with some success, the trains of morbid action, and, perhaps, give to each cause its proper place in his estimate of their agency in causing the disease. But, in some cases, he knows but little of the nature and 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 that 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 embarrass us in its treatment. They sometimes completely alter, either gradually or suddenly, the whole character of the case; and yet they may be the consequences of causes, which have been secretly, but surely, doing their work from the first onset of the disease. 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. Sometimes there are precursors of the full development, half showing themselves, and the watchful physician may discover in them the coming storm, long before the indications are manifest to the common observer. Even after convalescence has, to all appearance, fairly begun, and the symptoms seen during the progress of the disease are gone, some new symptoms may appear—the upshot of a train of morbid influences, which had been all the while imperceptibly advancing to this result; just as I have seen a fire, supposed to be extinguished, burst forth like a new fire in another part of the building, to which it had secretly made its way.