26 THE POPULAR SCIENCE MONTHLY 



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 some- 

 what 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 child- 

 hood 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 com- 

 position of a mixture of tissues suggesting similar combinations of 

 tissues which existed at such places some time during embryonic devel- 

 opment. 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, explain- 

 ing 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. Eecent investigations of Eobert 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, occur- 

 ring 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 pig- 

 mented moles. 



However, not all the tumors found in the first half of life develop on 



