The common history of impetigo is that after some degree of redness and tumefaction of the sldn, one or more distinct pustules slowly make their appearance, the irritation which accompanies them being so slight as to escape observation in most instances, and the eruption itself receiving little attention. The matter con tained in them very soon becomes decidedly purulent and forms a firm scab : but before those first observed have had time to dry up, others appear in succession, which are either scattered and distinct, or in close proximity to the former. It is scarcely pos sible to say, in the first instance, which of the two varieties is likely to be developed.
When the disease has already lasted some time, and a thick crust has formed, it matters little whether it be called eczema impetiginodes or impetigo—herpes it cannot be ; for the only question worth considering is, whether there be any. appearance of redness or tendency to spread about its margin. The crusts of dry pus, when solitary and rather large, are very like those of the next subdivi sion, ecthyma ; when in clusters, or covering a large siirface of the scalp, they can only be mistaken for favus. The scalp, and neck, and face, are the chief sites of impetigo figurate, which is more rarely seen on the limbs : impetigo sparse occurs chiefly on the back and arms, and less frequently on the legs.
In Ectlipna the pustules are large and solitary, although very often a number are found together on one limb, and none else where, showing thus a tendency to aggregation. . The g,reat dis tinction between it and impetigo independently of the difference of size in the pustules, seems to 'be that the cutaneous texture is more deeply affected : in the one there is an abraded surface which secretes pus, in the other there is a nearer approach to an ulcer under the dry crust with which it is covered. This brings it into close relation to rupia, which is only distinguished by the ulcera tion being more unequivocal, the scab larger and more adhering : in rupia, too, there is no tendency to aggregation, the scabs are few and solitary.
Ecthyma is seldom fonnd in the chronic form : it is easily distinguished from boils or carbuncle by the circumstance that it is quite superficial, and there is consequently no surrounding elevation of hard and tumid skin, as when the suppuration proceeds from the deeper textures. Nothing has been said of the syphilitic eruptions, because they must be taken by themselves, but it is worth noticing here that when there is much approach to ulceration this dis- • ease comes nearer in appearance to one of the common forms of secondary eruption than any we have yet had to refer to.
Acne and Sycosie are names applied to suppuration of the folli cle& The latter confined to that which appears at the roots of the hair in the beard, the former including all other cases. In this sense, every common pimple may be called acne ; but the name is reserved for cases in which there are so many as to show a general tendency to this kind of suppuration. Although the course of each individual pimple be not very prolonged, yet the progress of the disease is slow : not unfrequently, this tardiness is shown in persistent redness after the actual suppuration is at an end, and its continued re,currence in the same follicle& When such a blotchy redness alone remains, and no pustule is to be seen, a learner may be at a loss to what class he ought to refer the case ; its rugged surface renders it unlike eczema, and the absence of crust shows that it is not impetigo ; its redness and its posi tion, only on the face or back of the neck, prevent its being con founded with lichen or psoriasis : it is most apt to be taken for tubercle of the skin.
Sycosis much more nearly resembles impetigo : crusts generally form, and are very obstinate and adherent: but it is to be ob served that the skin is elevated round the crust, which is just what we should expect from the circumstance that the suppura tion proceeds from a follicle deeply seated in the cutis, and not from its surface.
Farus, which has been classed among pustules, we shall refer to its true place as a parasitic growth.
§ 6. Pemphigus or Pompholyx and Rupia.—These two disor ders, although very different in their history and causes, may con veniently be classed together, because they are characterized by the existence of bulk) (literally bubbles). In pemphigus the con tents of the bulla are always serous, in rupia puriform ; and they thus correspond in some measure to the division of the smaller eruptions into vesicular and pustular. In connection with this there is a similarity in history, the one appearing more frequently in an acute form, the other being always chronic; there is also a chronic pemphigus, to which the name pompholyx is given, to complete the analogy with chronic eczema.