Lichen Aestivus is an affection depending on an elevated temperature, and is naturally more frequent in tropical regions than elsewhere. In temperate climates, however, it prevails to a considerable extent during the summer months. The following classic description by Dr. Winter-bottom is taken from Willan's work (96, 57): "The Prickly Heat appears without any preceding disorder of the constitution. It consists of numerous papulae, about the size of a small pin's head, and elevated so as to produce a considerable roughness of the skin. The papulae are of a vivid red color, and often exhibit an irregular form, two or three of them being in many places united together; but no redness or inflammation ex-tends to the skin in the interstices of the papulae.

"The eruption is diffused over those parts of the body which are usually covered, as the neck, breast, arms, legs, and inside of the thighs. It does not appear on the face, excepting on the upper part of the forehead contiguous to the hair; neither is it ever found in the palms of the hands, soles of the feet, nor on the hairy scalp. The number of the papulae is much increased by wearing flannel, or clothes too warm and thick for the climate. When perspiration is very copious, small pearly pustules, containing a limpid humor, are often intermixed with the Prickly Heat, more especially on the breast, and about the wrists; but they terminate in scales, having no disposition to ulcerate, though scratched.

"A troublesome itching attends the Prickly Heat and prevents sleep during the night. There is likewise a frequent sensation of pricking, as if a number of pins were piercing the skin. This often takes place suddenly, after drinking a dish of tea or any warm liquor, so as to cause the person affected to start from his seat.

"The eruption is in general stationary, and appears equally vivid in the day and in the night. It does not leave one part and arise on another unless the former bo much exposed to cold, and the latter be heated by additional clothing, or by friction. An increase of heat indeed, in all cases, produces a greater number of papulae. They sometimes disappear on a sudden, and return again as suddenly, without any obvious cause; but whenever the eruption continues for a length of time, the papulae throw off minute scales, and are succeeded by a fresh crop, no vestiges being left in the skin.

"Persons of a fair complexion, with red hair and a soft skin, are most liable to this eruption and have the greatest quantity of it. Those who are of a dark complexion, either remain wholly free from the eruption, or are affected with it very slightly."

Diagnosis

The character of the eruption, taken together with the season of the year in which it occurs, obviate all difficulties in diagnosis, as there is no other eruption, except the strophulus of infants, that at all resembles it.

Etiology

A heated atmosphere is undoubtedly the exciting cause of the eruption, and this, taken in connection with too profuse perspiration, a full habit and a lack of cleanliness, constitute the main etiological factors.

Treatment

The treatment of Lichen AEstivus is very simple, and considerable relief can be afforded by attention to ordinary hygienic requirements. As a rule little, if anything, is required in the way of internal medication, and even if it were there is very little in the way of internal medication known to the writer that can be credited with being of much service. Both acid and alkaline drinks, fruit juices on the one hand, and carbonated alkaline waters on the other, exert perhaps a slight beneficial influence. External agencies are more important. The avoidance of unnecessary exposure to heat is to be first considered, next thorough cleanli-ness and the removal, by daily or twice daily baths, of the effete matters left upon the skin by the evaporation of the perspiration. Cold baths afford temporary relief, but the reaction is often followed by increased ir-ritation. On the other hand we have found baths as hot as could be borne afford more lasting comfort. Turkish baths have proved specially useful. A mild alkaline application, made by adding half a pound or more of or-dinary sal. soda to a full bath (thirty gallons) is sometimes very soothing.

When the eruption is not very extensive, sedative ointments or lotions stramonium. cherry-laurel, or chloral may be employed. In this connection my friend Dr. Bronson (201) has found lemon-juice an agreeable and useful application. In the severest cases bromide of potassium or small doses of opium may be required at night. 14