Pachyderm

“ The male differs from the female in his immense tusks, greater size, strength, and endurance; so great is the difference in these respects that the males when caught are valued at one-fifth more than the females. [12] The sexes of other pachydermatous animals differ very little or not at all, and, as far as known, they are not polygamists. Nor have I heard of any species in the Orders of Cheiroptera, Edentata, Insectivora and Rodents being polygamous, excepting that amongst the Rodents, the common rat, according to some rat-catchers, lives with several females. ”

“ The animal has no canines, sometimes no incisors even; sometimes it has as many as thirty-six teeth, according to the species, as naturalists aver; and this is all I have to say about this great lump of flesh, so misshapen outside, yet so regularly formed within. He it is who especially deserves the title pachydermata, his skin being so hard and thick that bullets glance off its surface. ”

“ For instance, if it be true among mammalia that the highest types, such as quadrumana, are essentially tropical, may it not be that the prevailing distribution of the inferior pachyderms within the same geographical limits is owing to the circumstance that their type was introduced upon earth during a warmer period in the history of our globe, and that their present location is in accordance with that fact, rather than related to their degree of organization? ”

“ Pach′yderm, thick-skinned—n. one of an order of non-ruminant, hoofed mammals, thick-skinned, as the elephant:—pl. Pach′yderms, or Pachyder′mata.—adj. Pachyder′matous, thick-skinned: insensible to impressions.—n. Pachyder′mia, a form of elephantiasis in which the skin becomes thick and warty.—adj. Pachyder′moid.—ns. Pachyē′mia, a thickening of the blood—also Pachyæ′mia; Pachy′ma, a genus of fungi consisting of tuber-like growths, some of which are now referred to the genus Polyporus—also Tuckahoe, Tuckahoe truffle, or Indian bread; Pachymē′nia, a thickening of the skin.—adj. ”

“ In addition to its constant formation of cells to replace those cast off from the surface, the active proliferation of the elements of the Malpighian layer is responsible for the development of the various appendages of the skin, the hairs with their sebaceous glands, the sweat glands, horny growths and the hoof, and, in the human subject, the nail. These occur as thickenings and down-growths of the epithelium into the corium.
The epidermis is devoid of bloodvessels, but is provided with fine nerve fibrils which ramify between the cells of the rete mucosum. ”

“ They are larger in many species than in man, and, in general, the sensibility of the tongue appears to diminish in proportion to the remoteness of the subject from the human structure. The epidermoid papillæ are separated from the tongue along with the epidermis, or rather, epithelium, by maceration for a few days in vinegar. They are pyramidal in form. They are grouped round the sensitive papillæ, except on the edges and point of the tongue, where they are rare. Their base is perforated, and always gives outlet to a crypta. ”

“ Describe parchment skin, and state the treatment.
Parchment skin (xeroderma pigmentosum, angioma pigmentosum et atrophicum) is a rare disease, the exact nature of which is not understood. It is characterized by the appearance of numerous disseminated, freckle-like pigment-spots, telangiectases, atrophied muscles, more or less shrinking and contraction of the integument, and followed, in most instances, by epitheliomatous tumors and ulceration, and finally death. It is usually slow in its course, beginning in childhood and lasting for years. ”

“ It is in the deeper layers of these cells that the pigment of the negro's skin is found. The fifth and deepest layer of the epidermis is the stratum germinativum, in which there is only one layer of columnar cells. The whole of the epidermis is non-vascular, and it will be noticed that as the different layers approach the surface the cells become more and more flattened. The true skin, dermis or corium is composed of a felted network of white fibrous tissue with a small number of yellow elastic fibres interspersed. ”

“ It is highly probable that the causes of these modifications of the epidermis in diverse groups of animals could be traced to the habits and modes of life of each, but I make no attempt here to do this. It is also matter for inquiry, upon which no agreement has apparently been reached, how it came to pass that man has virtually lost his hairy coat, and in regard to the palms and soles of animals, what may be the reason that so few have any hair on them, and why man has no sebaceous glands, but has very numerous sweat-glands in these regions. ”

“ Others, further advanced in development, are small, sessile, or pedunculated hard outgrowths, without bluish colour and sometimes covered by thickened epidermis. There is a large patch of pigmented (brown) skin on the dorsal surface of the right foot, and in the neighbourhood of this pigmented area are some minute nodules of similar character to those already described. It is possible that the pigmented skin has been the site of minute growths which have undergone spontaneous involution, and have, as frequently happens in Lichen planus, left pigmentation of the skin behind them. ”

“ They are whitish, grayish, or blackish in color, are rarely larger than a pinhead, each being pierced by a hair, around which are accumulated, in the form of strata, the horny cells of the epidermis. In some lesions the hair is broken off at the apex, appearing as a black central point; in others the hair is not visible, but is found coiled or twisted up within the papules. The skin is dry, harsh, or rough, and together with the papules may feel like a nutmeg-grater. ”

“ Remember that the fluid must act upon the inside of the skin, for the epidermis is often almost impervious to it. If you allow the skin to lie upon itself in thick folds, stuck together on the inside, those spots are liable to lose their hair in a most unaccountable and aggravating way. If the skin is small and thin, the bath soon does its work; but if it is a large skin, move it up and down, and all about, every day for the first two or three days. By the end of that time its preservation will be complete. ”

“ According to the layer-theory, these two layers are homologous throughout the series of Metazoa; their limits can always be accurately defined, they give rise to the same organs in all cases, and the adult organs (excluding the mesodermal organs) can be traced back to one or other of them with absolute precision. Thus the ectoderm gives rise to the epidermis, to the nervous system, and to the lining of the stomodaeum and proctodaeum, if such parts of the alimentary canal are present. The endoderm, on the other hand, gives rise to the lining of the enteron, and of the glands which open into it. ”

“ In chimaphila and uva-ursi there are no outgrowths from the epidermal cells.
In senna, witch-hazel, chestnut, and coca, numerous non-glandular hairs occur on the epidermis. In tobacco, belladonna, henbane, pennyroyal, peppermint, and spearmint both glandular and non-glandular hairs occur on the epidermis.
When studying leaves there should be considered the absence or presence of outgrowths and their nature; the nature of the epidermis and, when present, the number of layers of the hypodermis; the nature of the stoma, whether raised above, even with, or below the level of the epidermis ”

“ The lower epidermis consists of polygonal cells which are greatly elongated vertically and are drawn out into papillae (fig. 86) . Outer walls are thickened ; inner walls are also thickened except in some cases, when the upper epider- mal cells are divided by walls parallel to the surface. The lateral walls are thin and straight. The tendency to form a two-layered epidermis as well as the palisade-like elongation of the epidermal cells are adaptations to protect the palisade tissue against insolation as well as to check transpiration by depressing the stomata. ”

“ I have often raised up in many places the epidermis of an old person; it has not appeared to me to differ much from that of the adult; it is a little more subject to scale off and it is a little thicker. In some miserable objects which come to hospitals, there is often vermin in cracks of the epidermis, whose layers are afterwards separated by them and in which they live; so that I have seen the epidermis in this way conceal thousands of little animals, which were evidently found between the layers of this membrane, and which were not upon the reticular body and the papillæ. ”

“ Generally, the patches come out very gradually and in small numbers and, in the main, symmetrically, but as the older patches never go away spontaneously, while fresh ones are continually evoluting at short or long 120intervals, large areas are involved, and in the course of years (in one case, months) the whole trunk and limbs are crowded with lesions, though there are always spaces of normal skin intervening, or sometimes completely enclosed by the diseased process, where the original patches have coalesced. ”

“ The superficial layer, the epidermis or cuticle, is composed wholly of epithelial cells, of which the deepest layer is columnar and moulded upon the papillary layer of the derma, while the intermediate layers are more rounded and the surface ones flat. The deepest layer also contains the skin pigment, which causes the variation in shade between the Indian, the negro, and the white man. Below the epidermis, which is chiefly protective, is the tough, elastic, and flexible tissue of the derma or true skin, in which are vested most of the activities of the skin. ”

“ No blood-vessel is ever found in the epidermis, and hence, when you cut it, it never bleeds. As long as you live it is always growing. The top scales are always being rubbed off. Whenever you wash your hands, especially with soap, you wash off some of the top scales; and you would soon wash your skin away, were it not that new round cells are always being formed at the bottom of the epidermis, along the line at d (Fig. 15) , and always moving up to the top, where they become dried into scales. Thus the skin, or more strictly the epidermis, is always being renewed. ”

“ Development of the Tissue Systems.—In the growing plant the embryonic cells soon become differentiated into three primary meristem layers, known as dermatogen, periblem, and phloem, from which are developed respectively the primary cortex, epidermis, and the stele or vascular cylinder. The dermatogen forms the outermost layer of cells at the growing point, and when present always develops into true epidermal tissue. In stems the dermatogen is always single-layered, while in roots it consists of several layers and develops a many-layered epidermis. ”

“ Herbert Spencer [12] maintains that when muscles are much used, or when intermittent pressure is applied to the epidermis, an excess of nutritive matter exudes from the vessels, and that this gives additional development to the adjoining parts. That an increased flow of blood towards an organ leads to its greater development is probable, if not certain. Mr. Paget [13] thus accounts for the long, thick, and dark-coloured hair which occasionally grows, even in young children, near old-standing inflamed surfaces or fractured bones. ”

“ The eyelids are developed as ectodermal folds, which blend with one another about the third month and separate again before birth in Man (fig. 7, κ) . The lachrymal sac and duct are formed from solid ectodermal thickenings which later become canalized.
It will thus be seen that the optic nerve and retina are formed from the brain ectoderm; the lens, anterior epithelium of the cornea, skin of the eyelids, conjunctiva and lachrymal apparatus from the superficial ectoderm; while the sclerotic, choroid, vitreous and aqueous humours as well as the iris and cornea are derived from the mesoderm. ”

“ Every kind of animal sensibility is foreign to the epidermis. We know that it can be pricked, cut or torn, without being felt. It is especially on the palms of the hands and the soles of the feet that these experiments are easily made. The thickness of this membrane is such in this place, that we can remove layers of it, as we see done by those who try the edge of an instrument, that it is possible even, as most cooks do, to put it in contact with live coals, and that it is not impossible to carry a red hot iron over it. ”

“ The forehead and scalp are the favorite sites, but they may also occur elsewhere. The eruption is rather scanty as a rule, consisting usually of ten to thirty lesions. They begin as small maculo-papules, as papules, or as minute nodules in or on the skin, and gradually become small pea-sized, with a tendency to slight vesiculation or pustulation at the central part. The lesion is sluggish in its course, drying to a thin crust, which finally falls off, leaving a depressed variola-like scar. New lesions arise from time to time, and the disease thus continues almost indefinitely. ”

“ CHAPTER XIV. THE EPIDERMIS AND ITS DERIVATIVES. In many of the Cœlenterata the outermost layer of the blastoderm is converted as a whole into the skin or ectoderm. The cells composing it become no doubt in part differentiated into muscular elements and in part into nervous elements, &c.; but still it may remain through life as a simple external membrane. This membrane contains in itself indefinite potentialities for developing into various organs, and in all the true Triploblastica these potentialities are more or less realized. ”