DISEASES OF THE SKIN AND CELLULAR TISSUE - is pretty generally admitted that the information possessed by most practitioners of medicine in this department is exceed ingly vague : the lines of demarcation between the various forms are indefinite, and the results of treatment for the most part un satisfactory. It is true that in general the diseases of the skin are not of very great importance, but it is an erroneous conclusion that they will not therefore repay the trouble of study. Our failures in treatment are not unfrequently the result of ignorance, and a little pains bestowed on ascertaining the true principles of diagnosis, and acquiring an aptitude in discriminating the varie ties which these diseases present, will very soon enable the student to learn for himself what mode of treatment is useful in one form. useless or even hurtful in another. It will thus limit the choice of his remedies to a few that may do real good, in place of his ringing the changes in a variety of impotent drugs, to be at last relieved of a tedious and unmanageable case only by some acci dental change in the constitution of the patient which at once dissipates the local disorder.
On a superficial view nothing should be simpler than the diag nosis of skin diseases. If a man but use his eyes aright, it may be said, he ought to be able at once to distinguish them ; here is surely an instance in which the symptom is pathognomonic of the disease. In this, I believe, consists the great difficulty, and this short-sighted reasoning is one of the chief causes of the ignorance that prevails. If the scope and intention of the preceding pages have been made at all intelligible, no argument is needed to prove that skin diseases do not in this respect differ from others; they are by no means isolated facts in the economy ; and while we must acknowledge the faulty action in one tissue, we must not ignore it elsewhere. The evidence of the constitutional fault is, however, not always manifest, and when present, its language is not always the same. The symptoms which were enumerated in the early part of our inquiry, as indicating the general condition of the patient, have to be reviewed ; but though we find some preponderating more than others in particular classes of skin diseases, there are none which may be fairly classed as diagnostic of any individual disorder. We are thus forced to take up the two
subjects separately, and frame our diagnosis of the cutaneous affection, independently of the more general derangement of which it is chiefly a symptom ; and this limitation prevents our being able to correct the opinions based upon one set of observations by that derived from the other.
One rule may be given at the outset as applicable to all cases, and especially to those about which there is doubt, that the dis tinguishing characters are most readily traced in the commence- • ment of the disease, and the student should make it his business always to see the most recent spots of the eruption. This is in fact the history of the case, which is often written more correctly in the different patches on the skin of the patient than it is ever detailed in the most accurate case-book. Next in value to seeing the eruption at its earliest stage is a good account of it from the patient himself: and in this we have only to guard against asking leading questions, where interrogation is so necessary to elicit the facts at all.
In certain forms, concomitant fever may or may not exist, and in such it is essential to mark its presence or absence; but this rather with reference to treatment than to diagnosis, for we do not regard those as cutaneous diseases of which fever is an essen tial element ; we deal with it simply as one of the constitutional states which must be considered in its casual relation to the erup tion, of whatever nature, which is present.
§ 1. Erythema—Urticaria—Roaeola.—In subdividing the sub ject of this chapter, it will be most convenient to consider those forms, first, in which the epidermis is not altered ; the skin is red, perhaps elevated and tender, but its surface is unbroken.