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is a deformity or an imperfect development rather than a disease of the skin. Like all deformities, it is very apt to be hereditary, affecting one or more members of a family, and often skipping a generation. It is characterized by a marked deficiency of the normal cutaneous secretions and a tendency to the formation of a dry, scaly surface, which suggested the name of "fish-skin disease." It is sometimes congenital, may indeed develop in utero, but often does not manifest itself until several months after birth. In rare instances it may develop late in life. Though always improved by judicious treatment, it may be considered as one of the incurable dermatoses, since the peculiar character of the skin cannot be changed.

There are various degrees of severity in which ichthyosis may manifest itself, and different names applied to these have led to some confusion as to their true character. For instance, the term xeroderma, or "parchment skin," has been used unnecessarily to designate a very mild form of ichthyosis in which the skin presents a dry, mealy appearance, especially apt to be noticed in children with whom bathing is a rare luxury. In some cases this slight ichthyotic tendency disappears in time, and sometimes appears in later life as an acquired condition. It should be borne in mind that as the hair in some children is preternaturally dry and in others unusually oily, and that as this condition may vary in the same individual according to the state of health, so the degree of natural oiliness or dryness of the skin may vary greatly in individuals and in accordance with season and general condition. A skin which is notably dry and with a tendency to chap or roughen might be regarded as xerodermatous or ichthyotic in a very slight degree.

In ichthyosis mitis (or simplex) the characteristic features of the affection are well developed. The skin is dry, and perspi-