TUMOK. 530 TUMOR. normal tissues. While Cohnheim's hypothesis offers a very satisfactory explanation of most of the phenomena connected with the growth of tnmors, it uuist be remembered that it is as yet piirely a theory, with absolutely no basis in known facts : that no one has ever been able to demonstrate any of these little islands of embry- onal tissue lying dormant and waiting to be excited into tumor formation. Bacteria as the excitants of tumor formation have been exploited by some investigators. VhiIe some at present be- lieve that the true cause of cancer will ultimately be found to be bacterial in nature, the majority tend to the opinion that the presence of bacteria in tumors is an external accidental occurrence rather tlian an internal causative factor. Tumors grow ( 1 ) by direct extension from the periphery, and (2) by a growth of the tumor at its centre and a consequent pushing outward of its peripheral parts, or 'central growth.' (3) Tumors also extend by what is known as metas- tasis. This with the formation of what are known as metastatic tumors occurs by the dis- semination of cancer cells by means of the blood and lymph. In this way bits of cancer tissue are carried to remote parts of the 'body. Tliis met- astasis from a single primary focus may occur in any tissue or organ, and quite conunonly occurs in many tissues and organs either in succession or at approximately the same time. It is one of the surest evidences of the malignancy of the original tumor. These cancer cells lodging in the tissiies set up new centres of growth, of the same nature as the motlier growth. As the process of growth goes on in tumors so also does the pro- cess of degeneration. Tumors may ulcerate or become gangrenous, aljscesses may form in them, and they may undergo fatty or calcareous de- generation. Degenerative changes are more fre- quent in the softer more rapidly growing forms. Various classifications of tumors have been suggested, all of which are more or less un- satisfactory. Clinically, tumors are frequently simply divided into two classes : ( 1 ) benign tumors, or tumors which are in themselves harm- less, and (2) malignant tumors, as cancer and sarcoma. The most common and as yet most satisfactory classification of tumors is morpho- logical, based upon their structure relative to the normal body tissues. The following is the classification given in Delafield and Prudden'a Eandhook of Pathological Anatomy and nisiol- ogy (1902): CoNNECTIVE-TlSeCE TYPE. Normal Tissue. Form of Tumor. Fibrillar connective tissue : Fibroma. Mucous tif,sue : Myxoma. Embryonal connective tissue : Sarcoma. Endothelial cells : Endothelioma. Fat-tissue: Lipoma. Cartilage: Chondroma. Bone: Osteoma. Neuroglia: Olionia. Mdscle-Tissce Type. Smooth-muscle tissue : Leiomyoma. Striated-muscle tissue: Rhabdomyoma. Nerve-Tissue Type. Neuroglia. Vascular-Tissue Type. Blood vessels : Angioma. Lymph vessels: Lymphangioma. Epithelial-Tissue Type. Glands ; Adenoma. Various forms of epithelial cells andl „„„„.„„„ associated tissues: j- Carcinoma. Classification according to histogenesis (de- velopmental history of the tissues) has been at- tempted; and while there are reasons for believ- ing that embiyologj' may ultimately furnish the proper basis for tumor classification, that which it has thus far furnished is less satisfactory from a practical standpoint than the morphologi- cal classification. When, as is not infrequently the ease, more than one kind of tissue is present in a tumor, a combination of terms is used to designate its nature. Thus a combination of a tumor composed of embrj-onal connective tissue with a bony tumor is known as an osteo-sarcoma ; a muscle-tissue tumor in which mucli more than the usual amount of connective tissue is present, as a fibro-niyoma, etc. In addition to the new growths included in the classification given there are other forms of tumors or of structures some- times called tumors which do not fall within any of the subdivisions of the classification. Among these may be mentioned cysts of various kinds, including the so-called 'dermoid cj'st' and teratoma; such congenital tumors as moles, na?vi, and angiomata, etc. The peculiar placental tis- sue tumor known as deciduoma maj' also be men- tioned. Non-JIalignant Tumoes. These are composed of tissues of the types found in the adult and are in themselves not dangerous to life, although sometimes serious from pressure upon or involve- ment of important organs. They do not as a rule grow as rapidly as do malignant tumors: they do not tend to recur when completely removed, do not form metastases, do not involve neighboring lymph glands, and do not as a rule interfere with the ganeral health of the patient. Fibroma. — This tumor is composed of fibrillar connective tissue of the type found in the adult. Fibromata vary even more greatly in consistency than does ordinary fibrous tissue, those contain- ing many fibres and few cells being hard and firm, fibroma durum; those containing propor- tionately, many cells being soft, fibroma inolle. They are commonly inclosed in a definite fibrous capsule. The softer fibromata are frequently very vascular, while the harder forms usually contain few vessels. They are found in the skin and subcutaneous connective tissue, in the- connective tissue framework of the various or- gans, in the mucous membranes, in the intermus- cular septa, in nerve slieaths, etc. Mucous polypi of the nose are examples of this kind of tumor. Myxoma. — Jlyxomata are tumors composed of tissue which resembles a type of tissue found only in extremely small amount in the adult and known as mucous tissue. Mucous tissue is there- fore essentially embryonic. These tumors re- semble the fibromata in structure, being made up of connective-tissue cells Avith a fibrillar inter- cellular substance. The softer tumors are known as myxoma rjclatinosion. or myxoma moUc, while those of greater consistency are known as myxo- ma mcduUare. Jly.xoma is of comparatively rare occurrence in pure form. More commonly niyxo- mata are combined with tumor tissue of other types to form complex tumors of which the most common are lipo-myxoma and fibro-myxoma. They most frequently develop in fat. Lipoma. — Lipomata are fatt.v tumors. They ma}' be quite firm from the presence of fibrous tissue, fibro-lipoma. or soft, Vipomri molle. Lipo- ma is a very common form of tumor, being often
