The vesicles are superficial in situation, the firm papule which precedes the variolous rash being altogether wanting. They are at first transparent, their contents plainly showing through their translucent roof-wall, composed only of the stratum corneum of the epidermis. They are both acuminate and globular, and occasionally rest upon a slightly hyperæmic integument. Umbilication rapidly occurs at the apex, and simultaneously their contents become lactescent and gradually sero-purulent. Occasionally vesicles are transformed into genuine, coffee-bean-sized, pustules. Intermingled with these are often seen illy-developed and abortive vesicles.
By the end of a period lasting from twelve hours to the second or third day involution has usually begun, and the lesions, with and without rupture—more often the latter—desiccate, and are thus transformed into yellowish or yellowish and brown, circular, circumscribed crusts resting upon an apparently unaltered integument. These crusts are often so firmly attached that they do not fall spontaneously before the lapse of from five to eight days. When this exfoliation is ended there are left slightly hyperæmic pigmented patches of corresponding size where the crusts had rested. A destructive process occasionally results upon the surface of the face at the base of such vesiculo-pustular lesions as have formed there, in consequence of which a small depressed and superficial cicatrix is left, which does not differ from that resulting from discrete variola. These scars may be superficially seated and transitory in character, or much deeper and persistent through life.
Throughout the course of the disease systemic symptoms may be altogether wanting, or may occur in a mild, and much more rarely in a severe, type. In some cases the temperature is increased by one or two degrees upon the appearance of the exanthem, and often a febrile movement of moderate grade may persist for forty-eight hours or somewhat longer. Defervescence, however, is always rapid and perfect. In very rare cases there is a subsequent successive new development of scanty vesicles, whose appearance is heralded by mild exacerbations of fever.
Occasionally the vesicles may be recognized upon the mucous surfaces of the lips, inside of the cheeks, tongue, palate, conjunctivæ, and progenital regions of both sexes. Still more rarely the glands of the throat become slightly tumid and painful.
The complexus of symptoms, in the large majority of all these little patients, is that which pertains to a disorder of distinctly mild type. The eruptive lesions are scanty and productive of but trifling subjective sensations. Occasionally they are picked or scratched, and thus become the seat of either pain or pruritus. In the febrile stage the child is noticeably fretful for a period of perhaps twenty-four hours. At the end of that time older children are frequently observed engaged in their customary amusements in the nursery.
Severe types and complications of varicella are in general limited to the little patients who are recognized as suffering from hospitalism. Among these we see erysipelas, severe vaccinal eruptions, lesions of inherited syphilis, and the sequelæ of morebilli and scarlatina, which the disease both precedes and follows.
PATHOLOGY.—The anatomical structure of the lesions in varicella is largely a matter of inference, since there has been but small opportunity of studying the disorder as displayed in sections of the morbid integument. Manifestly, the exanthem is exudative in type, the serum in circumscribed areas lifting the superficial layer of the epidermis from the deeper parts of the derm. Unquestionably, septa occur in typically developed varicella chambers, similar to those seen in variola—a pathological fact which is the corner-stone of the doctrine relating to the unity of the two disorders. The serum contained in these septa possesses an alkaline reaction. The formation of a cicatrix is evidently due to the intensity of the process in certain exceptional lesions, as a result of which the papillæ of the corium are superficially destroyed. These sequelæ are often due to the picking and scratching of the lesions.
DIAGNOSIS.—Varicella is to be distinguished from eczema pustulosum by its mild febrile symptoms, the discreteness of its pustular lesions, the absence of itching, and of infiltration of the skin in patches, and its tendency to symmetrical development.
From impetigo and the impetigo contagiosa of Fox of London it will often be scarcely differentiated. Inasmuch as these disorders are frequently recognized among children suffering from varicella or varicella convalescence, it can scarcely be doubted that these diseases have been in the past often confounded, and that in many cases it is practically impossible to distinguish between them. Decided elevation of bodily temperature, umbilication of symmetrically-disposed lesions, and a rapid involution of the disease point to varicella. The two forms of impetigo occur without fever, are usually scantily developed, and are much more apt to be pustular in type, lacking, moreover, the halo of the varicella lesions. The latter are also, on an average, smaller and more numerous. The two forms of impetigo, finally, never display the generalized eruption of severe varicella. The non-contagious variety of impetigo is much more decidedly pustular in its lesions, and the latter spring from a deeper plane of the epidermis.
As to the eruptions due to vaccinia and vaccination, there can be but little doubt that these also have been frequently confounded with varicella. Efflorescences having origin in this way are very largely impetiginous in type, and the conditions named above are then to be regarded as distinctive differences, so far as any distinction can, under these circumstances, be recognized. Impetigo, impetigo contagiosa, and varicella are all sufficiently common accidents after vaccination. No reliance can be placed upon characteristics described as connected with a certain stuck-on appearance of the crust regarded by Fox as characteristic of the crusts in impetigo contagiosa. In all these vesiculo-pustular disorders of childhood desiccating serum and sero-pus upon the surface result in the formation of crusts which have a similar (so-called) stuck-on appearance.