Occasionally the reddened skin is dry, and covered with small scales : that this is not psoriasis is proved by the circumstances that the skin is evenly inflamed all over, and that the scales are not aggregated in patches which run into each other. As a con sequence of the inflammation, the skin is generally cracked and sometimes bleeds, and this never happens with psoriasis unless the scales be very thick and adherent, when the diagnosis cannot be difficult. This form of eczema is best seen in what is called "grocer's itch," or on the hands of washerwomen.
When the oozing from the surface, in place of continuing as a thin serosity, becomes purulent and hardens into crusts, the name eczema impetiginodes has been employed. It is quite unnecessary to distinguish this from real impetigo, for the diseases are closely analogous, except when the borders of the eruption are red and inflamed, and the eczema is spreading; if there be only a chronic purulent discharge the name given is quite immaterial.
The great characteristic of herpes is, that the vesicles are dis tributed in groups or clusters: they are also larger than those of eczema, and do not so readily fuse together. On their disruption the secretion almost always forms a gum-like scab ; their duration is commonly short.
Among its more constant forms we find the following: Herpes labialis occurring in one or two patches on the lips, sometimes on the nose, and more rarely about the eyelids ; in common parlance described as the effect of "a cold," and evidently associated with irritation of the mucous membrane. Herpes circinatus—one of the " ringworms" in which the clusters assume an annular form ; the vesication and the scab alike distinguish it from lichen circumacriptus and from lepra ; there can be no excuse for a mistake, except when the eruption is disappearing. Herpes zoster is only remarkable for Its situation, and the extent to which it may extend, encircling as it does the one-half of the trunk, and though generally bounded in a remarkable manner by the mesian line before or behind, yet sometimes passing beyond. Herpes preputialis is worthy of notice because it has been sometimes mistaken for chancre ; it has no peculiar characters to distinguish it from any other form of herpes; it is perfectly different from any syphilitic affection.
Patches of herpes wherever occurring, usually known as "shingles," except in the few instances enumerated, are so exactly like the eruption on the lip, which is familiarly known to every one, that description is unnecessary. It is often preceded by considerable local irritation, and a sort of cutaneous neuralgia very frequently remains after it has died away.
Scabies should not, perhaps, in a scientific work be classed as a vesicular disease, because the vesicle is really an accident, and may be replaced by a pustule. But for purposes of diagnosis it
is well to it in its present place, because whereas lichen, prurigo and the scaly diseases all have their chief site on the outer aides of the limbs and back of the trunk, the vesicular eruptions generally, and scabies in particular, select the inner aspects of the limbs and the flexures of the joints. The warns, which is the essence of the disease, does not inhabit the vesicle, but grooves out a curved channel for itself, which may be generally seen as a black line like the letter S: its presence always determines the eruption of solitary vesicles, which may in course of time become pustules; and them, are sure to be found at the flexure of the wrist or between the fingers, and along the inner side of the arm, wherever else they may be. One vesicle, with a distinct groove from it in such a situation, is enough for diagnosis, any amount of itching without these signs is of no value :. prurigo causes quite as much itching, and pustular, or even quasi-vesicular eruptions, occur very frequently among children of the lower classes which closely resembles scabies, and can only be pronounced not to be so by observing this remarkable predilection for locality and the constant presence of the groove when the parasite is really present.
§ 5. Pustular Eruptions.—A fully developed pustule is quite unlike anything else, but just as at certain stages of the vesicular eruptions the secretion is not serum, so in the pustular the secre tion is at first not true pus, and, after the pustule has burst and discharged, the crust may not be quite characteristic. In impetigo this difficulty is most likely to be met with, because its characters vary as the disease is spread over a large surface in solitary pustules, called impetigo sparsa, or is limited to distinct patches, when the name figurata is applied to it. In the former the single pustules have at first much the appearance of vesicles, but they very soon lose their transparency : among vesicular diseases we have found no such example except scabies; and, therefore, when a case of this kind is met with, the question cannot be, is it eczema which exists only in patches, or herpes which forms small and well-defined groups, but whether it be scabies or impetigo : the answer is only to be obtained from the diagnosis of scabies. When, again, the eruption occurs in patches it is more liable to be mistaken for herpes : but the course of the two diseases is quite different; the one commences suddenly, and is preceded by irritation, the other is gradual, and its beginning is unobserved : the one terminates in a few days, the other lingers on for weeks or months.