SIMPLE VASCULAR TISSUES.
Cellular Tissue.—Cellular pseudo-tissue is one of the most common of adventitious for mations, composed of associated white fibrous and yellow fibrous (elastic) fibrils. But rarely does it possess the character of the natural texture in perfection ; the distinction of its component filaments is less clear, the fasciculation of these less regular than in the typical structure. A more or less successful attempt at its production is made in all cases, where induration-matter forms, — the highest degree of perfection seems to be attained in old adhesions of serous membranes. A lapse of many months is necessary, however, to mould the new structure into its most perfect attainable form ; while on the other hand, a period of seven days (as we have seen in a fatal case of pleurisy) will suffice for the production of an imperfect tissue of this class.
Schwannt found that embryonic cellular tissue yields no glutin ; the same fact has been ascertained by Simont in respect of the adventitious cellular tissue of condylomata,— by Gueterbock, in respect of that of granula tions. The latter observer found pyin in the water in which the granulation-substance had been boiled. At an early period of for mation fibrin is found in association with the principle (tritoxide of protein ?) to which the name of pyin has been given ; eventually glu tin is yielded on ebullition, but it may be doubted whether the chemical constitution of the new, is ever precisely the same as that of the imitated texture.
Serous Tissue.—A single layer of polygonal pavement epithelium, beneath this a basement membrane of singular tenuity, and yet beneath this a stratum of cellular tissue, constitute a serous membrane. This structure is essen tially disposed to form shut sacs, and produce and retain a certain secretion. So far we have a texture which is often generated adventiti ously ; but if, as is now admitted, natural serous tissue is supplied in its proper sub stance with nerves*, it becomes a complex structure, of which a perfect adventitious copy is never generated.
A new serous sac may be produced (a) by modification of natural structure, with addi tion of a new element ; or (b) be completely adventitious.
(a) In this class appear those well known cases in which pressure, with or without fric tion, causes condensation of cellular tissue with production of epithelium, the latter form ing a lining for a sac of the former. So are produced new supernumerary bursm about the knees, the shoulders of porters, between the skin and hone of stumps, between the skin and spinous processes in spinal curvature, whether priinary or from caries, &c.
(b) Purely adventitious serous tissue is either (a) laminar or (b) saccular.
(a) By the laminar variety, we understand those strata of pseudo-serous tissue which invest false membranes in serous cavities.
(b) The saccular variety comprehends cysts, primary and secondaty. Printery cysts are spontaneously evolved, are capable of indefi nite increase in number and size, through some intrinsic force, constitute in themselves the disease where they exist, form the material they contain, are closed on all sides, lined with epithelium, and simple or compound.
Simple cysts occur singly or in clusters, and may appear in almost every region of the body ; their walls are of variable thickness and simply cellular, fibrous or calcareous ; their contents serous or glairy. The mamma and ovary are the most frequent seats of the clustered simple cyst.
The compound cyst (cystoma) is charac terised by its faculty of producing secondary cysts in its walls, — these a tertiary series and so on. Their closest investigator, Dr. Hodg kin, assigns them three chief varieties of form, — the pedunculated, the intermediate, and the broad-based, foe a full description of which we must refer the reader to his treatise.f The growth of the contained cysts is some times so active, as not only to give a nodulous outline to the main mass (which may attain enormous bulk), but to cause rupture of' the walls of the primary cyst. Various morbid changes, inflatnmatory and other, may arise in these productions ; carcinoma may even, in predisposed persons, be formed in their walls, but not (so far as evidence goes) be produced in their cavity as an evolution of blastema exuded from their lining membrane.