In the fourth place it is a well-known fact that nerve action may produce reflexes which not infrequently produce dermatitis. As to the influence of dentition upon skin affections, there is as yet no conclusive proof of there being a mutual eonnection, but it is generally coneeded that the period of dentition renders the skin more susceptible to pathological conditions.
Finally, it stands to reason that excessive or inferior nourishment exerts an unfavorable influence upon the skin. Badly nourished, atrophic or eaehectie children are more susceptible to skin diseases than healthy ones who are powerful enough to resist them. On the other hand, orernutrition, especially during the nursing period, is responsible for excessive fat cushions in aniumic children, thereby favoring disorders of the circulation and with it the appearance of eczema, a very frequent complaint and generally recognized tinder the name of milk eczema. By changing the conditions of nutrition, the eruption may be materially improved if not entirely cured.
Beside the physiological and injurious conditions of the skin, heredity —the hereditary family taint—causes quite a number of skin diseases, or is responsible for a tendency thereto. Tt is generally known that iehthyosis and other keratoses are a family affection and that xerodernia pigmcntosum and epidermolysis bullosa occur only in certain families. It is also a well-known fact that there is a special tendency for eczema in certain families, in some of which every' member responds by an eczematous eruption to an external irritation.
There is a close connection between heredity and diathesis as to the influence exercised upon the skin. Diathesis also is hereditary, although its action on a child is different from that on the adult. A scrofulous and lymphatie (exudative) cliathesis especially has an un doubted influence upon the skin. -Whoever has had an opportunity of observing scrofulous children with their tendency to catarrh of the eyes, chronic eoryza and enlargement of the glands, will know how frequently serofulous eczema with its characteristic general features occurs among them, how the eczema frequently opens the door to the tubercle baeillus and thus to scrofuloderma and invasions of lupus, and how a chronic nasal catarrh frequently changes into lupus of the nmeous membrane.
On the other hand, a lymphatic diathesis with its hyperplasia of the entire lymphatic apparatus, its enlargement of the spleen and lymphatic glands, hypertrophy of the palatal tonsils, and of the adenoid tissue in the nasopharyngeal space, prepares the soil for quite a series of skin affections.
The frequent occurrenee of rheumatic affections in erythema multi forme and nodosum has been ascribed by the French lespeeially Bazin, Besnier and others) to a eonnection with arthritic diathesis.