The accidental and non-essential elements of Growths belong to the other divisions of Adventitious Product. From the class Pre cipitates may be found saline matter, anior phous or crystalline, in minute quantity, or so abundant as to convert (in the instance of fibroma) portions of a Growth into true con cretions. Fat occurs in the various forms mentioned in a previous page; rare in some genera, as fibroma and enchondroma; it abounds in carcinoma. From the order De posits appear melanie matter and pus ; the latter an element generated by inflammation in Growths as in natural textures. Growths, too, of one kind may (as entozoa of one species grow in the bodies of another) find a nidus for development in Growths of a dif ferent kind ; cancer may thus appear within the area of an erectile tumour.
Exudation-Products exhibit themselves in the form of compound-aranule corpuscles and induration-matter ; while of Pseudo-tissues, there occur epithelium, cartilage, cellular, serous, fibrous, elastic, osseous, cutaneous, pilous, and dental tissues ; the last three limited to Cystoma.
The elementary cells of Growths may either lie in juxtaposition, or interspaces, filled with so-called intercell substance, may exist between tbem. This substance may be fluid or solid. Fluid intercell substance is nothing more than non-solidified blastema; the solid variety is amorphous, or composed of fibrous pseudo-tissue.
§ 4. The PavstoLoci' of Growths com prises the phenomena of their origin, en largement, decay, elimination, cicatrization and local reproduction, — phenomena which, it appears to us, can, only by misapprehension of their true relations, be included under the head of the Pathology of these Formations.
All that is known actually, or surmised upon fair grounds, concerning the origin of Growths, has already been stated in our gene ral remarks on Blastemal Formations.
The enlargentent of Growths is effected by the reception and evolution of nutritious matter. Growths receive this matter from vessels ; these vessels either permeate the mass generally, supply portions only of its substance, or merely reach a greater or less extent of its surface. In the first case, the growth is said to enlarge by intussusception ; in the third, by pure imbibition ; in the second, by both means. These distinctions are less important than they on first view seem ; the perfect nutrition of the extra-vascular natural tissues proves, as a general fact, the vigour and efficacy of the imbibition-process ; and in truth imbibition is at play in all nutritions, for the nutrient elements of vascular tissues must be imbibed through the coats of their vessels, and (it may be) in addition (as in the instance of the endosteal lining of the canals of Havers, and the subjacent osseous substance) through a stratum of cells. Enlargement by
intussusception differs therefore from that by imbibition, in degree rather than in kind. In whichever way conveyed to the seat of Gro wth formation, the nutrient material, at first fluid, is evolved and appropriated by continuous cell-generation. Now this cell-generation may be effected on an endogenous or an exo genous plan. When the plan is endogenous, the germs of young cells are contained and evolved within elder ones ; these secondary cells are endowed with a similar procreative faculty; the tertiary series are in like manner fecund, and so on. Here a single cell may be regarded as the potential embryo of an entire growth. When, on the other hand, the plan is exogenous, the germs of new cells are not found within, but lie, and are evolved, outside old ones.
Where endogenous evolution prevails, and a cell is, potentially considered, a tumour in futuro, the perpetual production of similar cells is easily intelligible ; the offspring that follows is as the parent that went before. But in exogenous Growths the continuous germination of infinite series of like cells is not readily conceived. It may be surmised (and the surmise amounts rather to a modified expression of the fact than an explanation), that when a series of cells has sprung into being, this series acts on the evolution of succeeding ones, as a natural vascularized surface is known to do on the generation of epithelium cells ; the formed series so in fluences newly-exuded blastema (of which it constantly excites the accession), that this shall produce a new series of cells similar to itself. But, however the perpetuation of like cells be understood, be it remembered that the thing itself has its limits ; for, as we have just seen, deposits may appear in Growths, pseudo-tissues are among their fre quent constituents, and a growth of one kind may establish itself a nidus within the area of another generically dissimilar.