Microscopical examination shows a marked increase in the pigment in the lowest layers of the rete mucosum, as well as more or less pigmentation in the corium usually following the course of the bloodvessels; in the verrucous variety the papillae are greatly hypertrophied, in addition to the increased pigmentation. There is, as a rule, more or less connective-tissue hypertrophy. #What is the treatment of naevus pigmentosus?# In many instances interference is scarcely called for, but when demanded consists in the removal of the formation either by the knife, by caustics, or by electrolysis. This last is, in the milder varieties at least, perhaps the best method, as it is less likely to be followed by disfiguring cicatrices. In naevus pilosus the removal of the hairs alone by electrolysis is not infrequently followed by a decided diminution of the pigmentation. In recent years both liquid air and carbon dioxide have also been used successfully in the removal of these growths. Pigmented naevi, which show the least tendency to growth or degenerative change, should be radically removed, as they not infrequently lead to carcinomatous and sarcomatous growths. #Ichthyosis.# (_Synonym:_ Fish-skin Disease.) #Give a descriptive definition of ichthyosis.# Ichthyosis is a chronic, hypertrophic disease, characterized by dryness and scaliness of the skin, with a variable amount of papillary growth. #At what age is ichthyosis first observed?# It is first noticed in infancy or early childhood. In rare instances it is congenital (ichthyosis congenita), and in such cases it is usually severe, and of a grave type; the children are, as a rule, prematurely born, and frequently do not survive many days or weeks. #What extent of surface is involved?# Usually the whole surface, but it is most marked upon the extensor surfaces of the arms and legs, especially at the elbows and knees; the face and scalp, in mild cases, often remain free. #Name the two varieties of ichthyosis usually described.# Ichthyosis simplex and ichthyosis hystrix, terms commonly employed to designate the mild and severe forms respectively. #Describe the clinical appearances of ichthyosis.# The milder forms of the disease may be so slight as to give rise to simple dryness or harshness of the skin (_xeroderma_); but as commonly met with it is more developed, more or less marked scaliness in the form of thin or somewhat thick epidermal plates being present. The papillae of the skin are often slightly hypertrophied. In slight cases the color of the scales is usually light and pearly; in the more marked examples it is dark gray, olive green or black. In the severe variety--ichthyosis hystrix--in addition to scaliness there is marked papillary hypertrophy, forming warty or spinous patches. This type is rare, and, as a rule, the surface involved is more or less limited. #Are there any inflammatory symptoms in ichthyosis?#