The tendency to psoriasis is frequently inherited, and often the disease may bo observed in two or more generations. Not infrequently it shows a tendency to skip a generation, and it has been claimed that psoriatic subjects are the offspring of eczematous, dyspeptic, asthmatic, gouty and rheumatic, as well as of psoriatic parents. External irritation only produces the disease in those who manifest a predisposition to it.
While it is often an easy matter to remove the eruption by treatment, it is difficult, if not impossible, in many cases, to prevent its speedy return. The eruption shows a marked tendency to relapse or to increase in severity in the spring or at some particular season, and in many cases persists for years or even throughout a lifetime. It often improves or disappears spontaneously for a few months or even for a year or more, and then reappears and continues its fluctuating course. The prognosis, therefore, is always a grave one as regards the permanent cure of the disease; but, in spite of the fact that some have declared psoriasis to be incurable, there are many cases which get well and remain well.
In the treatment of psoriasis a host of remedies have been employed, and many of them owe their repute to the fact, already stated, that the eruption tends at times to disappear spontaneously, and to any remedy employed at such a time the credit of a cure would naturally be awarded.
Among internal remedies, arsenic is the one most commonly employed and probably the most efficacious. In many cases, however, it may do much more harm than good. When the skin is irritable and the psoriatic patches congested, arsenic is worse than useless and alkaline diuretics are greatly to be preferred. But, on the other hand, when the disease is tending to get well, the administration of arsenic will often produce a most brilliant therapeutic result.
Of the various local remedies employed, chrysarobin stands without a rival. In many cases it produces a speedy and brilliant result which can be attained by no other local application. It has serious objections, however, which often forbid its use. When the skin is irritable it may cause the eruption to spread. Like arsenic, it is most likely to do good when the acute congestion of the psoriatic patches has subsided and the eruption is tending toward a spontaneous improvement. It not only stains the skin temporarily — which, however, is a matter of little importance — but it permanently discolors the underclothing and the bed linen, if due precaution is not taken. When
