rehead, and increases peripherally--the several
spots fusing together. The skin is peculiarly thin and easily
irritated. Exposure to the sun readily blisters it, and after the
slightest abrasion it bleeds freely. Several cases have been reported
in which the specific gravity of the urine was extremely high, due to
an excess of urea. Wood calls attention to the wave-like course of
leukoderma, receding on one side, increasing on the other. The fading
is gradual, and the margins may be abrupt or diffuse. The mucous
membranes are rosy. The functions of the swell-glands are unimpaired.

The theory of the absence of pigment causing a loss of the olfactory
sense, spoken of by Wallace, is not borne out by several observations
of Wood and others. Wilson says: "Leukasma is a neurosis, the result of
weakened innervation of the skin, the cause being commonly referable to
the organs of assimilation or reproduction." It is not a dermatitis, as
a dermatitis usually causes deposition of pigment. The rays of the sun
bronze the skin; mustard, cantharides, and many like irritants cause a
dermatitis, which is accompanied by a deposition of pigment.
Leukoderma is as common in housemaids as in field-laborers, and is in
no way attributable to exposure of sun or wind. True leukodermic
patches show no vascular changes, no infiltration, but a partial
obliteration of the rete mucosum. It has been ascribed to syphilis; but
syphilitic leukoderma is generally the result of cicatrices following
syphilitic ulceration.

Many observers have noticed that negroes become several degrees lighter
after syphilization; but no definite relation between syphilis and
leukoderma has yet been demonstrated in this race. Postmortem
examinations of leukodermic persons show no change in the suprarenal
capsule, a supposed organ of pigmentation.

Climate has no influence. It is seen in the Indians of the Isthmus of
Darien, the Hottentots, and the Icelanders. Why the cells of the rete
mucosum should have the function in some races of manufacturing or
attracting pigment in excess of those of other races, is in itself a
mystery. By his experiments on the pigment-cells of a frog Lister has
established the relation existing between these elements and
innervation, which formerly had been supposititious.

Doubtless a solution of the central control of pigmentation would
confirm the best theory of the cause of leukoderma--i.e., faulty
innervation of the skin. At present, w