Tumor (Lat. Tumere To Swell), an excessive growth of tissue confined to a limited region, not inflammatory. Tumors are described as "benign" or "malignant," as "homologous" or "heterologous." A benign tumor is one which does not, except by its mechanical action, interfere with life, and has generally no tendency to recur after removal. A malignant tumor is one produced by or inducing a constitutional taint, and usually reappearing after removal. A homologous tumor is one the structure of which is like tissues normally existing in the body. A heterologous tumor is one composed of tissues unlike to those normally present. Though a foundation of truth lies in this nomenclature of sufficient strength to have misled most physicians, our present knowledge of the histology and clinical histories of these growths has clearly shown that these distinctions are erroneous. The extremes are well marked, but the boundary line is irregular or confused. To what the growth of tumors can be ascribed is undetermined. That it is due to a perverted nutrition is certain, but how or why cannot be explained. The exciting cause is always mechanical, either from without or within the body; the predisposing cause, apart from heredity or mal-nutrition, specific or of other character, is obscure.

With such a knowledge of tumors, an accurate classification is impossible, but one can be made which will greatly assist in the diagnosis, prognosis, and treatment of these growths, and also in the examination of their minute structures, viz.: 1, cystic tumors; 2, those made up of simple or composite tissues, aggregated or arranged as usually found in the adult body; 3, those made up of simple tissues, aggregated or arranged in a manner deviating widely from the normal, the cell element largely predominating. A cystic tumor is one having a limiting membrane which exists normally, or is formed by a condensation of surrounding tissue, or is a production of new tissue. The contents may be fluid or solid. Housemaids' knee is an example of a fluid cystic tumor, the limiting membrane of which exists normally. The sebaceous tumor of the scalp is an example of one which is solid, produced by an obstruction in its duct to the secretion of a gland. A blow on the head may cause an effusion of blood beneath the scalp, which, by its outward pressure and irritation, can produce and excite the formation of a cyst wall. In this class will be comprised most ovarian tumors, kidney cysts, congenital tumors containing hair, etc.

To the second class belong all tumors of a fibrous, fatty, or cartilaginous nature, either alone or combined, and those made up of composite tissues, such as the vascular and glandular tumors. To the third class belong such growths as consist mainly of cells, or of cells mingled with other tissues in an irregular and abnormal manner: tubercle, sarcoma, cancer, etc. Making use of the terms employed in the nomenclature mentioned above, tumors in the first and second classes are homologous and generally benign; those in the third class are heterologous and as a rule malignant. - The chief interest, as regards prognosis, centres upon tumors of the third class. Opinion is divided as to whether cancer, using this term in its common signification, and taking this member of the class as the most important surgically, is primarily a local disease affecting the constitution only secondarily, or whether it is merely the local manifestation of a preexisting constitutional taint.