TUMOUR. It is not possible to define exactly the diseases which are commonly classed under the name of Tumours, and any definition in which the character of swelling (which is the true meaning of tumour) is included is unnatural ; for there are several diseases which agree in the most important respects with some of those called tumours, Lut are not attended by any obvious enlargement or swelling of the part in which they are situated; and the same disease exists in some cases with and in others without swelling. The greater part of the diseases which have been classed as tumours are examples of a large class of what may be called morbid or parasitic growths ; diseased structures, which are not mere alterations of previously existing parts, but new organisms or living substances which have grown within the tissues of the body by powers of development peculiar to themselves, and which depend upon the surrounding parts only for their supply of blood or other nutritive fluid. In this chess are included all those diseases described as solid or sarcomatous tumours, and those which are closely related to seine kinds of tumours, but are not accompanied by swelling, such as tubercle, certain forms of diffused cancerous growths, and some others.
The Leases called Encysted Tumours are entirely different from all others of the class in their pathological characters, and are considered in a separate article. [Was.] The chief cancerous growths are treated of under their appropriate heading [Ceascsa ; MELANOSIS] ; and tuber culous growths under the name of the disease which is consequent on their development [Purnisis ; Senor:Le]. The present article will be chiefly devoted to the history of those morbid growths which are commonly described as innocent tumours.
All morbid parasitic growths may be divided into malignant and innocent. The practical distinction between the two classes, from which they derive their names, is that an innocent growth or tumour is not likely to recur after being removed by operation, but a malig nant growth is likely to recur in the same or some other part. These two names may safely be retained to mark the two chief divisions of morbid growths ; • for although the test of the result of a surgical operation cannot be applied to those which from their locality do not admit of extirpation, yet the names indicate important characteristics in the progress of the two kinds of growth, wherever seated. Inde
pendently of the practical distinction, the most essential characters of malignant growths are :-1. That they may occur in almost any part of the Ludy, although some parts are more liable than others, and each kind of growth seems to find its moat appropriate seat ie a certain organ, as cancer in the breast, tubercle in the lungs, melanoais in the dc. 2. That they have a tendency to infect the adjacent parts, and to propagate themselves from one part to another, probably by germs carried from the primary disease into the blood, with which they circulate till they meet with an organ iu a fit state to supply them with the means of increase. 3. That they tend, through an intermediate process of softening (which appears to be consequent on the death of their constituent particles), towards ulceration ; that this ulceration is of a kind which is at present incurable ; and that in its progress it involves almost without distinction of tissue all the adjacent natural structures of the body, the particles of which, by their contact or combination with those of the malignant growth, seem first to assume a nature similar to their nature, and then to perish with them. 4. That in general the minute structures of which they are composed are dissimilar to those of the natural organs of the body; and that their development does not proceed to the formation of any structure similar to the fully developed tissues.
The distinctive characters of innocent growths are chiefly negative. Certain of them may present one, but they rarely present more than one, and never all, of the characters just described. Thus :-1. The number of tissues in which innocent growths occur is comparatively few : in many parts in which malignant growths are common they are never seen ; and when, as sometimes happens, many innocent tumours exist in the same body, they are (at least as a general rule) all found in the same tissue, or in or near the same organ. Thus, many fatty tumours may grow at the same time, but they all lie in the tissue of the natural fat : many fibrous tumours may occur together, but all are in or near the uterus. On the contrary, when many cancerous growths co-exist, they are commonly found in many different organs and tissues.