A tumour is a swelling or new production, and not a part of the original composition of the body. Blood may have been effused, and the coagulated part, becoming organised, is increased in size by deposits from the vessels which enter it; or perhaps the blood, the coloured part of it at all events, is taken up and lymph is deposited, which, if not also removed, “undergoes further changes of a secondary nature, and remains a parasite or new structure.” Its structure and growth are modified according to the action which its own vessels assume, independently of the surrounding vascular system. The bloodvessels may enter this new growth by a narrow pedicle; or it may be of such a form as to present an extensive surface, by which it communicates with the surrounding parts, receiving vascular ramifications from them. As the growth of the tumour proceeds, the surrounding parts yield, are condensed, and form an envelope for the new formation; the neighbouring bloodvessels are excited to a greater degree of action, and more blood is poured into the vessels of the tumour; the action of these in turn is very vigorous, and the increase of the new growth is more and more rapid. They become, it would appear, dilated and tortuous. Morbid enlargement, or rather new productions, often attain an enormous size; some have weighed, when recent, upwards of 60 or 70 lbs. Tumours differ much in structure; and though their general appearance may not be dissimilar, one will scarcely be found exactly resembling another. In many cases, the external appearance proves no certain index of the nature of the tumour; sometimes, however, its feel and general external character lead the experienced surgeon to form a correct estimate of its internal structure. It is impossible, by any process of reasoning, to account for the different actions which these growths possess; and even minute anatomical investigation, either of healthy or morbid structures, has not as yet thrown much light upon the subject.