TUMORS. 



(is occasional association, since in the great majority of cases these 

 conditions are not followed by tumors, nor, furthermore, has it ever been 

 possible to induce genuine tumors experimentally under these readily 

 secured conditions in animals. The bearing of trauma upon the origin 

 of tumors is to be held in mind in estimating the influence of sex, since 

 males are in general more liable to injuries than females. 



The relatively common development of tumors in pigmented and 

 other nsevi of the skin illustrates the significance of local malformations 

 as predisposing factors in the origin of tumors. ' 



Several cases have been recorded in which through injury there has 

 been a mechanical displacement of cells heterotopla from which in 

 their new situation tumors have developed. These cases, which have 

 been in a measure paralleled by experiments in animals, illustrate an 

 important class of congenital tumors, often cystic in character, which 

 arise from embryonal cell displacement, or, as is the case in many of the 

 tumors of the neck at the site of the branchial clefts, from an imperfect 

 closure of embryonal openings. 



We have seen that such evident malformation as the nsevi of the skin 

 may form the starting-point of malignant tumors. We know that in 

 many cases cells or tissues or parts of organs displaced during embryonal 

 life, as in the branchial clefts or in the kidney, may later develop into 

 tumors. Cohuheim has gone further than this and framed an hypothesis 

 to the effect that all true tumors are due to faulty embryonal develop- 

 ment. In accordance with this hypothesis, cells which in the course of 

 the development of the body may be displaced or become superfluous or 

 do not undergo the usual changes, may remain for long periods unaltered 

 but liable in later life, from whatever reason, to commence growing with 

 all the potencies of lowly organized cells in the midst of the mature tis- 

 sues. The noteworthy influence of heredity in the occurrence of some 

 tumors, the congenital nature and early development of others, their 

 atypical structure in general, and the tendency of many forms to occur 

 in situations in which during the development of the embryo consider- 

 able complexity exists, as well as their frequent primary multiplicity 

 all of these characters of tumors lend considerable plausibility to Cohn- 

 iieim's hypothesis, and it appears to be applicable in certain cases. But 

 it still lacks a morphological basis, since no one has seen the postulated, 

 strayed, or dormant embryonic cells ; again, it by no means follows be- 

 cause tumors often develop at the seat of malformations or may arise in 

 embryonal heterotopias that all tumors are thus associated ; and finally, 

 the frequent origin of epitheliomata in cells which have been formed in 

 adult life, in cicatrices, for example, is evidence that this hypothesis is 

 'not in any event of universal application. 



1 It should be remembered that many of the complex tissue growths often reckoned 

 among tumors and called teratomata are really embryonic rudiments of another indi- 



vidual. While such rudimentary embryos may be large and present such diversity and 



gement of tissue as to render the character of the growth obvio 

 the other hand, be very simple in character, as in some of the so-called dermoid cysts 



arrangement of tissue as to render the character of the growth obvious, they may, on 

 the other hand, be very simple in character, as in some of the so-called der 

 These are all to be regarded rather as malformations than as genuine tumors. 



