40 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS nearly every dopa-positive cell may show dendrites, whiie in the native and silver section very few may be seen. The striking and often bizarre forms of fully developed dendritic cells, as they are seen between the other pigmented and nonpigmented epidermal cells, may lead them to appear different from the other epi- dermal cells. They remind one very much of the melanophores of coldblooded animals. Especially in dopa preparations 'they have a striking resemblance to certain cells of the central nervous system. The peculiar morphologic characteristics of the dendritic cells have led many investigators to occupy 'themselves with the problem of their origin and function. In the course of time, various theories have arisen about their genesis and function. It is not necessary in the present state of the problem to discuss the views of the older authors (Schwalbe (7), Rabl (7) and Adachi (25)) who maintained that they are not cells at all but artefacts due to the pig- ment in the intercellular spaces. That the view was false was clearly indicated by the regularity of the demonstration of the nuclei of the cells. There are three main theories which still remain for discussion. Most of the investigators who have occupied themselves with this prob- lem support the view that the den- dritic cells are closely connected with melanin production. This point of view is supported chiefly by the fact that dendritic cells usually contain pigment and are especially numerous during active pigment production. Among the supporters of the theory of the pigment function of the dendritic cells there are di- vergences of opinion about their genesis. Especially the older authors, in analogy to the melano- phores of coldblooded animals, con- sidered the dendritic cells as pig- ment cells of mesodermal origin which had wandered up into the epi•termis in embyonal life, and had remained there to function a melanoblasts (Ranvier (7), Kol- liker (7), Ehrmann (2) and Del Rio Hortega aa)). Still others (Bloch (7), Miescher (29), Kreibich (34)) considered them as cells of ecto- dermal nature which are nothing more than special functional phases of ordinary pigment-building basal cells. According to S. W. Becker the melanoblasts of the epidermis do not rise from the ordinary basal cells (2.6). The French authors (Masson (28), Pautrier, Levy and Diss (35) and ,Caudiere (86)) went still further. They separated the dendritic cells completely from the rest of the epi- dermal cells. The older theory of Masson (19), which was accepted by Pautrier, Levy and Diss, ascribed a metabolic function to the den- dritic cells. As "cellules embo- ceptrices" they have the property of takif•g propig•.nents and various other substances from the reticulo- endothelial cells of the curls into the epidermis and of carrying away again from the epidermis into the

THE PIGMENT MELANIN OF THE SKIN AND HAIR 41 cutis waste elements or formed prod- ucts. This function, however, has not been proved. In the more recent papers of Masson (37), the dendritic cells have been classified as nerve cells and have been made identical with the Langerhans cells. A great deal of confusion has arisen because of the nomenclature used by various authors in writing about dendridc cells. In compari- son with the pigment-forming cells of the lower animals they have been called chromatophores or melano- phores. Still greater misunder- standing has been caused by their being called Langerhans cells (Masson (28 and 37), Pautrier, I,evy and Diss (35), Caudiere (36)), which are epidermal nerve elements and are not melanoblasts. As was shown by Bloch (7), quite apart from the question whether the den- dritic cells are closely allied or have their origin from nervous elements, they cannot be identified with the I•angerhans cells. This point will be taken up later. The terms in the following studies are those used by the Bloch school i.e., melanoblasts, pigment-building cells of the epi- dermis of dendritic or nondendritic forin and chromatophores, cells found in the cutis which phago- cytose pigment and are not pigment builders. The last-n, amed cells never show a positive dopa reaction, in contradistinction to the melano- blasts of mesodermal origin, which may also be found in the cutis in such conditions as blue nevus and mongolian spots. [)EI'IGMENrFATION BY •PECIFIC AN•I IOXIDANTS It was observed by Oettel (3S) in 1936 that the peroral actnfinistration of hydroquinone to black-haired cats turned the hair gray. Discon- tinuation of the drug resulted in repigmentation of the hair. In an investigation of occupational leuko- derma by Oliver, Schwartz and Warren (39 and 40), Schwartz found that the monobenzyl ether of hydroquinone, contained as an anti- oxidant in the rubber gloves of the workers, was responsible for the depigmentation. Their experi- ments as well as our own demon- strated that the alepigmentation was due to the action of.monobenzyl hydroquinone on the system "dopa"-oxidase dihydroxyphenyl- alanine ("dopa") (4l). Extensive experiments to study the mechanism of this depigmen- tation were carried out by Peck and Sobotka. (41). In a number of human subjects, both white and colored, the monobenzyl compound was applied in the form of a 50 per cent ointmentor as a 50 per cent ethereal suspension. In a few instances the concentrated powder was used. Leukoderma was pro- duced after incubation periods w•ry- ing from weeks. to months. Histologic examination of the areas of alepigmentation revealed a negative "dopa" reaction and an almost complete disappearance of the melanin. The microscopic pic- ture could not be differentiated from a vitiligo in many instances since the depigmentation was seen to