TUMORS SOMETIMES BENIGN, SOMETIMES MALIGNANT. Endothelioma.—These tumors orig inate from that type of connective tissue known as endothelium which forms the linings of blood vessels, lymphatics, etc. On account of their extremely cellular character and on ac count of the reduction of their intercellular base ment substance to a minimum, these tumors bear a close morphological resemblance to the carcinomata, among which they are often classed.
Endotheliomata are most common in the pleura, peritoneum, Jura mater, and pia mater. Less frequently they occur in brain, liver, ovaries, testicle. lymph nodes, salivary glands, bdue, and skin. They may be large or small, single or multiple, and may form metastases.
Adrnoma.—Adcnolnata are epithelial tumors in which the epithelium is glandular in type and is arranged in more or less distinct alveoli. They thus correspond in structure to a gland. The alveoli are supported as tumors in the irregu larity of the arrangement of their component elements. Blocking up of the ducts of the
glandular tissue sometimes leads to an accumu lation of secretion within the alveoli and the formation of cysts. When this cyst formation is a prominent feature of the growth the term cyst-adenoma is used to designate the tumor. (if these the most important is the multilocular cyst-adenoma of the ovary. Most adenomata are non-malignant, rather slow growing tumors. The most common sites are the ovary, mammary gland, kidney, liver. submaxillary, sublingual, parotid, thyroid, and lachrymal. They also (welly in those mucous membranes which are supplied with glands, as for example the mucous mem branes of the stomach, intestines, nose, pharynx, etc. The most common sites of malignant adeno mata are the stomach, intestines, mammary gland thyroid, and uterus.