even in the buccal cavity; however most frequently they are found in the ovaries and testicles. In these tumors are observed a great variety not only of ordinary tissues but of incompletely developed organs, as brain, eye, lungs, gut. These structures represent evidently malformed embryos. At first they grow usually slowly—in contradistinction to the typical mixed kidney tumors of children—but not infrequently somewhat later in life one or several of their constituent parts begin to assume a malignant growth, and even produce metastases.
Now the large majority of these tumors which appear in early childhood are in all probability congenital, they were preformed before the child was born; they are, however, usually noticed only at a time when they begin to grow somewhat more rapidly, and this may take place many years after birth; thus the sacral embryomata are often noticed first somewhere between the fifteenth and twenty-fifth years, when they begin to enlarge a little, and certain kidney tumors developing in all probability from misplaced embryonal adrenal tissue may even not become apparent until later in life. We may furthermore conclude that these congenital tumors of childhood and young adult life are in part due to localized aberrations during embryonic development, their composition of a mixture of tissues suggesting similar combinations of tissues which existed at such places some time during embryonic development. At that period certain tissues did not differentiate normally, did not become a functionating part of the organism restricted in its growth—but somehow preserved a part of the proliferative power which not fully differentiated embryonic cells usually possess and they exerted a destructive influence on the otherwise normally developed organism. The famous pathologist Cohnheim especially emphasized this origin of tumors; but he and still more so some of his pupils and followers extended the significance of their observations too far, explaining on this basis the origin of tumors in general, while their conclusion applies in all probability only to that class of tumors which appear in childhood and early adult life and perhaps to certain other related tumors. Recent investigations of Robert Meyer and others have indeed shown that certain minor embryonic malformations, especially in the region of the kidneys, the thyroid, thymus and eye are quite frequent; but that in the large majority of cases they certainly do not lead to tumor formation.
Other more or less benign tumors, which are often multiple, occurring simultaneously at different places are also frequently congenital, as for instance, growths consisting of lymph or blood vessels, cartilage, muscle tissue developing around small blood vessels, and fibrous tissue growths around nerves in certain areas of the body, furthermore pigmented moles.
However, not all the tumors found in the first half of life develop on
