The conditions of localization of Growths are curious, and for the most part inexplicable. The following propositions may be laid down concerning them : — (a.) The tendency to become the seat of Growths, as a class, varies greatly in the dif ferent tissues and organs. Thus, while cel lular tissue is their peculiarly favourite site, fibrous texture but rarely affords them a nidus. Again, the mamma, the ovary, the uterus, are frequent, the lungs and brain much less common, sufferers.
(b.) The tendency to become the seat of Growths, as a class, varies in the different parts of organs. Thus the pyloric end of the stomach suffers more frequently than the rest of the organ ; the epididyrnis than the body of the testis.
(c.) Certain organs, and certain parts of organs, have an excess of tendency to the formation of certain special Growths. Thus the uterus, the mamma, the stomach, the liver, are peculiarly prone to cancerous, as distinguished from other forms of growth ; the bones are the chosen seat of enchondroma. And, again, cancer does not form indifferently in all parts of the uterus, but tends especially to invade its neck ; while fibrous tumours affect a preference for the body of the organ. The large intestine is a tolerably common seat of cancer ; the small is very rarely implicated.
(d.) Growths of different kinds exhibit dif ferent degrees of compatibility as co-existences in the same body. Some Growths, as Cystoma and Carcinoma, are sufficiently prone to appear in the same individual; others, as Fibroma and Carcinoma, are rare co-exist ences; none are actually' incompatible, either as unconnected co-existences, or as develop ments in each other.* Sex influences the site of Growths. The renal organs of the male suffer more fre quently than those of the female ; the con verse is true of the genital organs. In like manner, age has its influence. But on the whole, the causes of these peculiarities of seat are unfathomed.
A Growth having once been developed, may pursue an anatomical (or better, topo graphical) course, of three different kinds. First, it may remain solitary and alone till the death of the individual in whom it exists, no other organ or tissue than that originally af fected becoming involved by similar disease. This is frequently observed in the case of enchondroma and of cystoid tumours, occa sionally of fibrous, and even of cancerous Growths.
Or, secondly, a morbid mass originates in some particular site, whence it seems to spread as from a centre to a multitude of parts ; the latter are said to be the subject of secondary Growths. The mechanism of this propagation differs according as parts adjacent to or dis tant from the primary formation are the con secutive sufferers. (1.) When circumjacent tissues become the seat of secondary develop ment, this is either the result : — first, of pro gressive and direct infiltration of those tissues by the morbid matter ; or next, of infiltration spreading to those tissues through the me dium of the proceeds of common inflam mation (induration-matter) previously depo sited among them, in some instances effecting adhesions between parts not actually adherent to each other in the natural state ; or, lastly, possibly of infiltration arising in some unex plained way, through the influence of a part simply placed in juxtaposition, and not con tinuous (either naturally or accidentally) with the tissues primarily affected. These modes of secondary implication are exemplified by cancer alone. (2.) The formation of second ary Growths in distant organs, where an effect of pre-existing disease elsewhere, seems only intelligible as a result of transmission by the lymphatic or vascular systems. Cancerous, and perhaps fibrous tumours, give rise through both these routes, to secondary development. As respects the lymphatic glands in commu nication with a cancerous mass, they may themselves become cancerous, while the ves sels leading to them are either filled with morbid matter of the same kind, or perfectly free from all anatomical change. Now when
the tubes are themselves loaded with cancer ous substance, and are, for example, traceable so loaded even to the thoracic duct (A. Cooper ; Hourmann), without any evidence existing of the matter being a product of their owu tissue, the implication of the lymphatic system, is evidently the result of absorption. But when (as is more commonly the fact) the cancerous state of the glands is unasso ciated with similar contamination of the con necting tubes, it is not thus so plainly and sa tisfactoril.17 explicable. Still it is probable that in the majority of cases the principle is even here the same ; but that the mode in which stagnation of absorbed particles takes place differs. In other instances it is possible that cancerous development in the glands may be effected as in an independent and original centre of production, and not through a pro cess of absorption or other direct mode cf influence of pre-existing Growths. These no tions are put hypothetically; but they appear to me more likely to be well founded than those usually tendered. Nevertheless if contamina tion be admitted to arise as a result of absorp tion in some instances, the inference appears necessary, that it shall occur in all cases ; inas much as a process of nutrition, accomplished in the usual way, is constantly going forward in morbid Growths. Now, as matter of fact, such contamination does not always ensue, and, above all, does not cominence from the earliest period of evolution of the previous growth. Here eems to lie a serious objection to the doctrine of lymphatic absorption. But the absorption is only thus shown to be of a kind which we may, for convenience sake, call unproductive; and which may be assimilated to that taking place from abscesses, in cases where no pus, with its sum of natural proper ties, finds. its way into the circulation. That the pus-corpuscles undergo, in such cases, disr integration and alteration, is matter of physical demonstration — changes which divest them apparently of their pathological properties. On analogy, which seems in nowise strained, we may then admit that disintegration of the elementary cells of the morbid Growth is the cause of the occasionally unproductive cha racter of cancerous absorption.* When, on the other hand, secondary Growths form in localities free from direct lymphatic commu nication with the seat of the primary forma tion, there can be no doubt (although the productive elements have not yet been found in transitu with the circulating blood) that the venous system acts as the agent of trans lation of such elements from the one to the other site. In the instance of cancer the following arguments may be adduced in favour of this notion. a. " Cancerous matter exists in a multitude of cases in the veins of the diseased part ; now this is obviously a most favourable circumstance for its circulation with the re turning blood. B. The rapidity of the suc cessive development of the disease in different organs, sometimes observed, seems only pro ducible by the agency of a fluid which, like the blood, pervades them all. 7. The liver and lung, the two organs in which foreign bodies introduced into the circulation are almost invariably observed to stagnate, are by far the most frequent seats of the secondary development of carcinoma. a. The parenchy matous viscera and the bones, the precise structures most frequently affected with se condary abscess, are those peculiarly liable to secondary cancer. e. In respect of both mor bid products, the liver and lungs stand at the head of the list for frequency of implication.