PRODUCTS, ADVENTITIOUS.—The difficulty of defining the term Adventitious Product with precision has so frequently been acknowledged, that we feel extremely diffident in offering a new attempt to the consideration of morbid anatomists ; the more so as the re cent disclosures of the microscope would pro bably strike the generality of persons as having, almost of necessity, simplified the task, while they have in reality rather in creased its perplexity. Fully conscious, then, of the debatableness of the ground we tread on, we would apply the term Adventitious Product to any substance which, either pro duced by or developed in connection with the animal franie, neither forms a natural consti tuent element, nor a natural secretive product, of the structures amid which it is evolved. The qualification, " either produced by or deve loped in connection with the animal frame" is required to ensure the exclusion of Foreign Bodies ; and the latter member of that quali fication, " developed in connection with the animal frame," as plainly necessary to ensure the inclusion of Parasites, which (whether they be the proceeds of equivocal generation or evolved from germs introduced from with out) are certainly not produced by the textures containing them.
Understood thus, (and the signification seems the widest that can, in a practical point of view, be given to the terra,) the character of adventitiousness is conceived to arise in three different ways: — a substance may, in truth, be adventitious, because its nature is different from that of any of the natural tex tures and secreted materials ; or because the form it has assumed differs from that under which it naturally occurs ; or because the situa tion it occupies is one to which such substance is in the natural order of things wholly foreign. Thus tuberculous matter is adventitious, be cause it differs in nature from all the elementary structures and secretions ; a calculus com posed of lithate of ammonia is adventitious, because the form, assumed by the salt compos ing it, differs from that it wears as a constituent of healthy urine ; and an ossification of the pleura is adventitious, because the ossiforrn structure forming it occupies a locality in hich, in the healthy state, bone is unknown.
The amount of adventitious quality in pro ducts of these three kinds differs: it is greatest and most clearly degned, where dependent on the nature of the constituent material. Thus, in the first place, concerning the adventitious ness of cancer or pus, no doubt can ever arise; their physical and chemical characters and their essential nature are decisive of the point. In
the second place, when a product becomes ad ventitious simply from the peculiarity of its localization, the question is often less dear ; nor indeed can. it in the existing state of know ledge be invariably settled. Muscular fibres have, for instance, been met with in the walls of the ureter ; albumen is excreted in great quantity with the urine in certain states of dis ease: but whether such muscular fibres are to be considered eticlences of hypertrophy or ac tual new products, and whether such albumen must be viewed as a totally new material of renal secretion, or as a natural element of urine in excess, depends upon the mode of decision of the preliminary questions, whether rudimen tary muscular fibres do or do not naturally exist in the situation referred to, and whether albu men do or do not, in excessively small propor tion, form a natural constituent of human urine. And this is not the only aspect under which it becomes practically difficult to distinguish hy pertrophous from adventitious products. The two states are in some conditions of disease distinctly and intimately associated. Thus, in eburnation of the heads of bones, the proper osseous tissue undergoes hypertrophy only, while the adjacent articular cartilage becomes infiltrated with adventitious bone. Again, the fat, which forms in abundance in the liver in the so-called " fatty degeneration " of that organ, is at first merely an excess of that naturally existing in the hepatic cells, and can there fore only be regarded as a product of unhealthy supersecretion : but with the advance of the morbid change, the inter-cell texture of the organ becomes infiltrated with fat ; and this fat is an adventitious product by reason of the lo cality it occupies. Nature here, as elsewhere, transgresses the artificial Ihnits established for the facilities of study. In the third place, it is clear that newness of form implies the quality of adventitiousness in an inferior degree only — that a material naturally existing dissolved in a secreted fluid, for example, does not, when from physical or chemical causes it accumulates in solid masses, possess the quality in question to the same amount as another which is never, under any shape nor even in the minutest pro portion, a natural existence.