Sclerenchyma

“ As examples the stems of Panicum flavidum, Panicum colonum, Panicum Crus-galli and Panicum fluitans may be considered. The stem of Panicum flavidum is broadly ovate in cross section with a flat front and is more or less solid, though occasionally the parenchymatous cells in the centre get broken. Two rows of vascular bundles surround a fairly large amount of parenchymatous cells of the ground tissue. There is a continuous ring of sclerenchyma separated from the epidermis by a fairly broad cortex. The cortex has a number of fairly large air-cavities separated by bands of parenchymatous cells. ”

“ Internal secretory organs are represented by tannin sacs occurring in the middle of the mesophyll, in cortex and pith.
The veins are embedded. The veins of the mid-rib are protect- ed on the lower side by strands of sclerenchyma.
The hairy covering consists of a few unicellular clothing hairs. Glandular hairs are not found.
Structure of the Axis: — The cortex is characterised by subepi- dermal cork. Some of the cells of the tanniniferous cortical parenchyma near the pericyclic stone-tissue contain solitary crystals of oxalate of lime. ”

“ The greater number of the parenchymatous cells are loaded with small starch granules, or in young and fresh barks with chlorophyll. In several barks, as in that of C. lancifolia Mutis, numerous cells of the middle cortical layer and even of the medullary rays, are provided with somewhat thick walls, and contain either a soft brown mass or crystalline oxalate of calcium. These cells have therefore been called resin-cells and crystal-cells; they are mostly isolated, not forming extensive groups or zones, and their walls are not strongly thickened as in true sclerenchymatous tissue. ”

“ Microscopic Structure—On a transverse section the bark exhibits some layers of cork-cells, loaded with brown colouring matter, and then, within the middle zone of the bark, a comparatively thick layer of sclerenchymatous tissue. Strong liber-fibres are scattered through the interior of the cortical tissue, but are not distributed so as to form wedge-shaped rays as met with in liquorice. In the latter the sclerenchyme (thick-walled cells) is wanting. ”

“ Winter’s Bark has a short, almost earthy fracture, an intolerably pungent burning taste, and an odour which can only be described as terebinthinous. When fresh its smell may be more agreeable. The descriptions of Clusius, as alluded to above, are perfectly agreeing and even his figures as nearly as might be expected.
Microscopic Structure—In full-grown specimens the most striking fact is the predominance of sclerenchymatous cells. The tissue moreover contains numerous large oil-ducts, chiefly in the inner portion of the large medullary rays. ”

“ Axis slightly ribbed, ribs strengthened by a few sclerenchymatous fibres. Epidermal cells of the axis tabular with outer walls greatly thickened and cuticularised. Cortex formed of chlorophyll containing parenchyma. Pericycle composed of large groups of stone-cells. Wood formed of xylem bundles separated by broad medullary rays extending to the cortical chlorenchyma. Groups of cells resembling bast fibres on the inner face of the xylem bundles. Pith composed of thick-walled cells. ”

“ In the case of marked sclerosis, the opening need not be large because, if the bone between the cortex and the antrum be solid, it is hardly probable that infection can spread through it to any outlying cells in the tip of the mastoid or elsewhere. ”

“ In patients with scleroderma, there is an excess production of collagen, the main fibrous component of connective tissue. As a result, the formation of dense, compact tissue causes the skin to lose its elasticity. Scleroderma is also a disease of the vascular and immune systems and can impair internal organs, such as the kidneys, lungs, heart, and gastrointestinal tract.
New biomedical research findings and innovative approaches to diagnosis and treatment are essential in fighting against this multifaceted disorder. ”

“ Diffuse symmetric scleroderma, or hide-bound disease, is quite rare, and presents itself in two phases: that of infiltration (more properly called hypertrophy) and atrophy, caused by shrinkage. The whole body may be involved, and each joint may be fixed as the skin over it becomes rigid. The muscles may be implicated independently of the skin, or simultaneously, and they give the resemblance of rigor mortis. The whole skin is so hard as to suggest the idea of a frozen corpse, without the coldness, the temperature being only slightly subnormal. The skin can neither be pitted nor pinched. ”

“ The chronic nature of the affection depends mainly upon the tendency that the inflammation has to recur in successive patches at different parts of the sclera. Often only one eye at a time is affected. Each patch lasts for a month or two and is succeeded by another after an interval of varying duration. Months or years may elapse between the attacks. The cicatricial site of a previous patch is rarely again attacked. The scleral infiltration causes a firm swelling, often sensitive to touch, over which the conjunctiva is freely movable. The overlying conjunctiva is always injected. ”

“ The Sclerotic (from scleros, hard) is composed of dense, white fibrous tissue, and gives to the eyeball its firmness of figure and its white color; in front, it constitutes the part commonly called "the white of the eye." It is one of the strongest tissues in the body; it possesses very few vessels, and is not very sensitive. It affords protection to the extremely delicate interior parts of the eye; and the little muscles which effect its movements are inserted into the sclerotic a short distance behind the cornea (see Fig. 48, Y, Z) . It is perforated posteriorly to admit the optic nerve. ”

“ In the diffusely lardaceous spleen the organ is enlarged throughout, pitting to pressure, and upon section presenting a waxy, semi-translucent appearance, usually of a reddish-gray, but sometimes of a deep-red, color. Instead of a pulpy, easily broken-down condition of the splenic parenchyma, there will be found a dense tissue that can be cut into tough, glistening slices. Minor degrees of the change cannot be readily detected by the unaided eye, and even in advanced cases the judgment will often be at fault. ”

“ Microscopic Structure—The uniform, small-celled, angular parenchyme is interrupted by numerous brown oil-cells of larger size. The inner part of the tissue contains also thin brown vascular bundles. The cells of the epidermis on either side are colourless, thick-walled, longitudinally extended, and covered with a peculiar cuticle of [Pg 509] broad, flat, riband-like cells, which cannot however be removed as a continuous film. The parenchyme is loaded with small granules, to which a red colour is imparted by Millon’s test (solution of mercurous nitrate) and an orange hue by iodine. ”

“ The wood-parenchyma is less abundant than the tracheids and fibers, and predominates in the more vascular parts; after two to four or more fibers in a radial row a single parenchyma cell may often be seen, but other arrangements occur. In the parts where fewer vessels occur it is not uncommon to find a series of radial rows of about six to ten fibers end in a single parenchyma cell, and thus are formed short, tangential rows of wood-parenchyma cells, intercalated, as it were, between the radial rows of other elements (Fig. 12, p) . ”

“ Less frequently the trabecular framework is added to by the formation of new bone, resulting in a remarkable degree of sclerosis, and if, following upon this, there is caseation of the tubercle and death of the affected portion of bone, there results a sequestrum often of considerable size and characteristic shape, which, because of the sclerosis and surrounding endarteritis, is exceedingly slow in separating. ”

“ The conversion of non-embryonic connective-tissue cells into muscle cells in the higher types has been described, but very much more evidence is required before it can be accepted as a common occurrence.
In addition to the probably degraded Dicyemidæ and Orthonectidæ, the Cœlenterata are the only group in which a true mesoblast is not always present. In other words, the Cœlenterata are the only group in which there is not found in the embryo an undifferentiated group of cells from which the majority of the organs situated between the epidermis and the alimentary epithelium are developed. ”

“ The space between the various branches of the canal-system is occupied by a gelatinous ground-substance (mesogloea) in which amoeboid and connective-tissue cells are embedded (fig. 34, 3, 4, 5; fig. 35, a) , and in which in most cases a well-developed skeleton is secreted by special cells known as scleroblasts. This skeleton (figs. 24-32, &c.) supports the extremely soft tissues of which the body is composed, and consists either of mineral spicules (carbonate of lime or silica) or of horny fibres (spongin) , or of a combination of siliceous spicules with spongin. ”

“ The vascular tunic may be congested in young infants, but atrophy soon [Pg 55] develops and may reach an extreme degree. The sclera ordinarily becomes quite thin throughout, but may retain almost a normal thickness at the equator of the globe and posteriorly. Posterior sclera ectasae may develop. The iris, as a rule, hangs free from the cornea, often tremulous because of retraction of the lens beyond the iris plane. In some cases the iris is partly or totally adherent to the posterior surface of the cornea. ”

“ Scleroderma. (Synonyms: Sclerema; Scleriasis; Dermatosclerosis; Morphœa; Keloid of Addison.)
What is scleroderma?
Scleroderma is an acute or chronic disease of the skin characterized by a localized or general, more or less diffuse, usually pigmented, rigid, stiffened, indurated or hide-bound condition.
Morphœa, by some formerly thought to be a distinct affection, is now believed to be a form of scleroderma; as typically met with it is characterized by one or more rounded, oval, or elongate, coin- to palm-sized, pinkish, or whitish ivory-looking patches. ”

“ The former closely resemble the amoeboid white blood corpuscles, or leucocytes, of higher animals, and have the power of wandering about from place to place in the sponge-wall. They probably serve to distribute food material and carry away waste products, and some of them undoubtedly give rise to the ova and spermatozoa. The scleroblasts are derived from cells of the dermal epithelium which migrate inwards into the gelatinous ground-substance and there secrete the spicules of which the skeleton is composed. ”

“ The sternum and ribs are most frequently affected in this way. There are instances in which the bone-marrow has not been involved, and in one case there was osteo-sclerosis.135 Histologically, the chief change is hyperplasia of the colorless marrow-cells, which in the pyoid variety compose the chief part of the tissue. They vary much in size and appearance. Three forms can usually be recognized: large granular cells with distinct nuclei; medium-sized cells, like colorless blood-corpuscles; and smaller forms, like lymph-cells, with large nuclei and a narrow zone of investing protoplasm. ”

“ There are also thick-walled bast fibres (Fig. 82) in the bast that serve for support. (3) There is also some parenchyma in the new bast; it is now in part a storage tissue. Sometimes [67] the walls of parenchyma cells in the cortex thicken at the corners and form brace cells (Fig. 83) (collenchyma) for support; sometimes the whole wall is thickened, forming grit cells or stone cells (Fig. 84; examples in tough parts of pear, or in stone of fruits) . ”

“ With a Graefe’s knife the fibres of the sclerotic are carefully divided in an oblique direction forward until the suprachoroidal lymph-space is opened for about 3 mm. The first part of the incision is performed with the blade and completed with the point of the knife, the anterior flap of sclerotic being held forward by straight iris forceps. Heine uses a keratome, dividing the fibres of the sclerotic with the point by stroking it along the line of the incision. The depth of the incision should be carefully gauged from time to time with the iris spatula ”

“ It is, however, unlikely that the fresh brain- and cord-tissue, when the site of disseminated sclerosis, will appear perfectly healthy to the naked eye under fairly good illumination. Much less intense lesions than those of disseminated sclerosis reveal their presence by changes in color and consistency. ”

“ Both eyes are almost always attacked. It more generally occurs in young people, mostly in young women. Deep scleritis is more persistent and less subject to periods of intermission than episcleritis. The deeper and more wide-spread inflammatory infiltrations of the sclera lead eventually to weakening of that coat, and cause it to yield to the intra-ocular pressure. Vision suffers from extension of the infiltration to the cornea, or from iritis with its attendant synechiae, or from anterior choroiditis, and sometimes also from secondary glaucoma. ”

“ In Fig. 12, a branching-out bundle of muscular fibre, taken from the upper lip of the rat, is seen to end in stellate connective cells. The delicate homogeneous sheath that binds the fibres together is termed sarcolemma. This is readily seen in prepared muscle of the frog and water-beetle, less plainly in man. Each muscle is provided with a sheath of connective tissue; this surrounds it, binds the fasciculi together, and supports the blood-vessels; it is called the perimysium, and sends fine prolongations in between the fibres, termed endomysium. ”