Melanocyte

“ Yet from the very happy circumstance of the conspicuousness of the pigment, the results of their activity could be observed with the utmost facility, and their behaviour in relation to inflammatory congestion easily studied even under a low magnifying power.
The pigment cells pervade the skin and subcutaneous tissue of which the frog's web consists, and are especially numerous about the blood-vessels, round which their branches twine abundantly. They must, therefore, be acted on along with the vascular parietes by anything applied to the surface of the membrane. ”

“ While dark-haired people show pigmentation in a very marked manner, those with red hair show it slightly or not at all. In some peculiar manner red-­haired people appear to possess a comparative immunity to the effects of intestinal stasis. Except for the face, the areas that show pigmentation most conspicuously are those exposed to friction, such as the inner aspects of the upper parts of the thighs, with the adjacent opposing surfaces of the buttock, the spines and abdomen where the corset or dress presses, the axillary folds, the bend of the elbow, and the neck. ”

“ Melanosis of the liver is comparatively frequent, especially in gray horses, and above all when they are aging and passing from dark gray to white. In many cases a more certain diagnosis can be made than in sarcoma for the reason that primary melanotic neoplasms are especially likely to occur on or near the naturally dark portions of the skin, as beneath the tail, around the anus or vulva, in the perineum, sheath, eyelids, axilla, etc. The extent of the disease is likely to be striking, the liver, next to the spleen, being the greatest internal centre for melanosis. ”

“ In spring, as the days grow longer and the nights shorter, the increasing amount of light received day by day through the eyes stimulates the pituitary gland to produce the gonadotropic hormone which directly or indirectly, stimulates molt and, probably by enzyme action, the melanoblasts are caused to be present in cells of the hair follicle and the melanoblasts provide granules of melanin pigment which are incorporated in cells of the growing hair. These granules of pigment give the hair its color. ”

“ Eiselt of Prague called attention to the fact that in cases of melanotic cancer of the liver, melanine appears in the renal secretion.20 When the urine is passed it is usually quite clear; but after standing it becomes of a dark colour, even as dark as porter, without, however, losing its transparency. This deepening of the colour is no doubt due to the oxidation of the melanotic pigment, as the employment of an oxidizing agent, such as nitric or chromic acid, causes the same change to occur instantly. ”

“ Melanism is an anomaly, the exact contrary of the preceding. It is characterized by the presence in the tissues and skin of an excessive amount of pigment. True total melanism is unknown in man, in whom is only observed partial melanism, characterized simply by a pronounced coloration of part of the integument.
Some curious instances have been related of an infant with a two-colored face, and of others with one side of the face white and the other black; whether they were cases of partial albinism or partial melanism cannot be ascertained from the descriptions. ”

“ Dried and dead cells are constantly and in great numbers thrown off from the surface of the skin: such epidermic appendages as the hair and nails grow and are removed, millions of cells are represented in the beard which is daily removed. Cells are constantly being destroyed on the intestinal surface and in the glands. There is an enormous destruction of the blood cells constantly taking place, certain essential pigments, as that of the bile, being formed from the hæmoglobin which the red blood corpuscles contain and which becomes available on their destruction. ”

“ It seems to be settled that the red color of blood is owing to iron contained in the red blood-cells, while it is established as a fact that the sun's rays are metallic, having "vapor of iron" as one element. It is also true that want of light causes a diminution of the red and an increase of the imperfect white blood-cells, and that this sometimes results in a disease called leucoemia, while all who live in the dark have pale and waxy skins, and flabby, weak muscles. Thus it would seem that it is the sun that imparts the iron and color to the blood. ”

“ Describe the vesicular type of dermatitis herpetiformis.
This is the common clinical type of the disease, and is characterized by pin-head to pea-sized, rounded or irregularly-shaped, distended or flattened and stellate vesicles, occurring, for the most part, in irregular and segmental groups of three or more lesions, seated either upon apparently normal integument or upon hyperæmic or inflammatory skin. They exhibit no tendency to spontaneous rupture, but after remaining a shorter or longer time, are broken or disappear by absorption. The lesions tend to appear in crops. ”

“ The internal layer is the rete mucosum. It lies immediately upon the true skin, and consists solely and wholly of cells, being equally destitute of vessels and nerves. Here begin the first discrepancies in the opinion of writers. Some deny that it belongs to the epidermis, looking upon it as a separate substantive tissue, neither skin nor scarf-skin, but intermediate to the two. Others find it only in the coloured families of mankind. It occurs, however, universally; being of a yellowish-white colour in Europeans, and dark brown or black in negroes, Indians, and the so-called dark races. ”

“ These facts explain malarial pigmentation and oligocythœmia.—— The facts just mentioned explain the origin and nature of malarial pigmentation, and also, in part at least, the oligocythæmia of the malarial state, which, as pointed out, is only partially accounted for by the destruction of corpuscles by the parasite in the general circulation as represented by finger blood. They show that what is seen in finger blood does not represent anything like the aggregate mortality that is going on among the corpuscles from direct destruction. ”

“ In as much as the minute capillaries end at the termination of the true skin, when putrefaction and fermentation begin there is an oozing of water from the capillaries and the surrounding tissues, between the two layers of skin, causing a blister to form, and known as skin slip.
At the lowest part of the false skin is a layer of germinal cells, from which all the other cells are derived, and becoming more flattened and horny as they are pushed farther away from the blood supply; and also a layer of pigment cells, which give the discriminating color to the skin. ”

“ Describe the symptoms of tinea versicolor.
The disease begins as one or more yellowish macular points; these, in the course of weeks or months, gradually extend, and, together with other patches that arise, may form a more or less continuous sheet of eruption. There is slight scaliness, always insignificant and furfuraceous in character, and at times, except upon close inspection, scarcely perceptible. The color of the patches is pale or brownish-yellow; in rare instances, in those of delicate skin, there may be more or less hyperæmia, and in consequence the eruption is of a reddish tinge. ”

“ The congenital growth rarely increases in extent, except as the body grows larger, but often the pigmentation becomes more pronounced and the hair begins to grow coarser in adult life. The development of small hairy moles upon the face of elderly
Fig. 29.
women, especially those suffering from hypertrichosis, is very frequently noted.
In the treatment of the pigmentary mole, acids or the electrolytic needle may be employed. For small, round, dark spots on the skin a minute drop of nitric acid, applied with a wooden toothpick, will often suffice to remove the blemish. ”

“ The patient becomes intensely weak, muscular movement becomes impossible, intellectual processes cause great fatigue, and finally blood pressure becomes so low that fatal collapse ensues from lack of blood in the brain. The external symptoms of these cases is a pigmentation, that is, a very dark discolouration of the skin, which develops rather early in the disease. The tongue especially becomes a very dark brown. Areas of pigmentation also occur where the skin is irritated,—at the wrists from the irritation of the coat sleeves, at the edge of the hair from the irritation of the hat. ”

“ The cells in question are minute microscopic structures, so small that we can not at all see them with the naked eye, but which have a habit of feeding in the body upon the various parts thereof whenever they get a chance. Cells of this sort go by the scientific name of phagocytes, which is merely a Greek term for 'eating cells.' The phagocytes, for instance, devour pigment in the hair, and in old persons the production of white hair has resulted from the activity of phagocytes which have eaten the pigment which should have remained in the hair and kept its color. ”

“ The fugitive paleness, which accompanies the coldness of the extremities, is owing to a less quantity of blood passing through the capillaries of the skin in a given time; where the absorbent power of the veins is at the same time much diminished, a part of the blood lingers at their junction with the capillary arteries, and a bluish tinge is mixed with the paleness; as is seen in the loose skin under the eye-lids, and is always a mark of temporary debility. ”

“ In the course of the next four-and-twenty hours in some cases, and in others not until the expiration of two or three days, it completely covers the body; not being confined exclusively to the skin, but frequently extending to the mouth and throat, and even to the external membrane of the eye.
In the course of two or three days from their first appearance the little pimples, increasing in size, will be found to contain a thin transparent fluid, to pit or become depressed in their centre, and the skin in the spaces between them will be found red. ”

“ Melanoma has a mortality rate of 25 percent and causes 5,000 deaths per year, and nonmelanoma skin cancer causes another 2,000 deaths per year. The 1983 National Institutes of Health Consensus Conference on Precursors to Malignant Melanoma found that the incidence of melanoma and the number of deaths from melanoma are increasing in many areas of the world and found evidence that early recognition and surgical removal of melanoma make it a highly curable cancer. ”

“ Extravascular pigment.——In the early stages of malarial disease, except in the case of the spleen and the bone marrow, pigment is entirely confined to the lumen of the vessels and to their endothelium. But if we examine tissues from a case which has died at a late period of the disease, the pigment may then be found, not only in the endothelium, but also in the walls of the vessels, and even in the perivascular lymph spaces, whence, it may be inferred, it is subsequently carried to the lymphatic glands to be finally dealt with and broken up. ”

“ 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. ”

“ Sun exposure is an undisputed cause of nonmelanoma skin cancer and is an important factor in the development of melanoma. The number of skin cancers can be reduced through sun protection measures such as the use of sunscreening lotions and simple changes in lifestyle. The American Academy of Dermatology and State and local dermatologic organizations are committed to heightening the awareness and understanding of melanoma and nonmelanoma skin cancers among members of the general public and the health care community. ”

“ In the former diseases, when several patches are close together, the normal skin between appears, in comparison, pale, and if cursorily examined might be mistaken for the pale patches of vitiligo, while the surrounding yellowish patches of tinea versicolor or chloasma may appear as the pigmented borders. In tinea versicolor the patches are slightly scaly. In morphoea there is always structural change.
Treatment in most cases is unsatisfactory. The functions and the state of the general health must receive attention. In some cases arsenic long continued proves of benefit. ”

“ The last and greatest achievement of medical science is not recorded in these pages. It is only recorded in ourselves. For that blue pigmentation in your eyes and fingers is due to the Sarakoff-Harden bacillus which closes once and for all the chapter of medicine. ”

“ On gray horses that at 10 or 12 years of age are turning white in color, purple-black malignant growths, known as pigment of melanotic tumors, frequently appear where the skin is black in color, and constitute the disease termed melanosis. ”

“ The pigment which gives the characteristic colour to the skin is deposited in the protoplasm of the outer ends of the cells in the form of small granules. An attempt is made to shew this in fig. 32.
At the apex of most, if not all, the primary wart-like papillæ there are present oval aggregations, or masses of epidermis cells, each such mass being enclosed in a thickish capsule (fig. 31) . ”