The Bradshaw Lecture ON MELANOSIS (MELANIN: MELANOMA: MELANOTIC CANCER): Delivered before The Royal College of Surgeons on November 8th
Authors: W. G. Spencer
Journal: BMJ (1923)

THE subject of this lecture, Melaniosis, in somiie of its aspects has engaged the attention of former lecturers and of con- tributors to the Museum of the College.I propose to relate briefly some recent observations from which there has been obtained an increase of knowledge as well as indications of the lines along which further research is desirable.Some races of mankind have developed a pigment, melanin, which together with a free secretion from the skin serves to protect the, central nervous system against the effects of excess of sunlight, and enables such races to work under the sun in the tropics, because the pigment prevents injury from the ultra-violet light rays.Races inhabiting colder regions, with much less pigment in the skin, have scattered collections of pigmented cells-melanomas.These have the characteristics of " congenital rests," which, although they show no outward change, yet as life goes on unidergo an insidious degeneration.Without any sharp line of demarcation the degeneration may pass to the formation of a new growth-melanotic cancer.Subject to individual differences this malignant chanige tends to arise in the later periods of life.In -horses which turn white with age melanotic cancer supervenes with inereasinig frequency the longer the animal lives.In man melanotic cancer is a relatively rare form, but it has the peculiarity that two factors are associated-a proliferation of cells and a multiplication of the melanin pigment.The degeneration of the " congenital rest " into melanotic cancer cannot be prevented, nior the further course of the disease controlled.Olnce the malignant change has started, even although there is lno clinical manifestation of it, a metastasis sets in forthwith.The secoudary growths,-however, displace rather than infiltrate, so that the metastasis may not become apparent for a long while.In addition to those oni tlhe surface there are collections of pigmented cells scattered in deeper structures which may be likewise regarded as " congenital rests."Through various causes, nioreover, pigmented patches may be acquired which also may tend to undergo malignant degeneration.Recent chemical observations have overcome to a large extent the difficulties concerning the analysis of melanin.A colourless melanogen-by oxidation becomes a coloured melanin and is closely allied in composition to adrenaline.Both are connected with other -protein derivatives which have the' same feature-that of changing into coloured substances as the result of oxidation.Used as histological stains some of these serve to demonstrate the presence of melanogen in epithelial cells by converting it into melanin.Again, substances contained in coal tar, allied to those derived from proteins, when introduced into animals cause melanin to form, as well as giving rise to cancer.Concerning the history of melanosis I limit myself to noting some of the contributors to the Museum and former lecturers.Hunter examined the skin of a negro by macerating it, and found that it separated into three layers-corneous, mucous, and fibrous; the pigment was situated in the mucous layer, which rapidly liquefied and the pigment then collected as a sediment.The skin on the dorsum of the negro's foot was deeply pigmented, that on the sole hardly pigmented at all.The same layer in the skin -of a whiti boy became