TUMORS. 297 



good for tumors of the individual organs. For e^mplejjzumors of the 

 stomach and of the tongue and lips are more frequentj" mftn than in 

 women. On the other hand, tumors of the breast arc far more common 

 in women than in men. 



Heredity. While the influence of heredity is difficult to estimate ac- 

 curately, there are a few well -authenticated instances of the remarkable 

 prevalence of malignant tumors in families within a few generations. 

 The general facts, however, are not so striking. The statistics of Wil- 

 liams showed that in two hundred and thirty-five cases of carcinoma of 

 the uterus or breast, about nine per cent, gave a history of carcinoma in 

 father or mother, while in nearly twenty per cent, there was evidence of 

 carcinoma in the family. In the estimates of other observers, the hered- 

 itary influence seemed evident in about one-third or one-fourth of the 

 cases. It is, however, instructive in this connection to note that in a 

 study by Snow, of seventy-eight healthy persons there was evidence of 

 carcinoma in the family in about one-fifth of the cases. 



It is clear, therefore, that while such statistics are suggestive and on 

 the whole indicate that an hereditary predisposition to the development 

 of tumors may exist, this does not in any way account for the immediate 

 incitement of the growth of tumors, and is indeed, as Meuetrier has urged, 

 but one of many examples of hereditary predisposition which is observed 

 in many forms of disease, such as infectious, cerebral apoplexy, etc. 



The influence of climate, food, race, and social condition has been in- 

 voked as bearing upon predisposition to the growth of tumors ; but the 

 evidence is not convincing that these are very significant in etiology. 



Local Predisposing Factors. When we turn from the general to the local 

 conditions bearing upon the origin of tumors, we find an imposing array 

 of instances in which tumors, and especially malignant tumors, follow 

 local injuries, either mechanical or toxic, or are associated with chronic 

 inflammatory processes. Bruises or contusions, particularly those in- 

 volving the bones, are not infrequently followed by malignant tumors, 

 and it is noteworthy that these tumors are most apt to be of the connec- 

 tive-tissue type sarcoma, osteo-sarcoma, chondroma, etc. Epithelial 

 tumors, on the other hand, are more frequently developed at the seat of 

 repeated injury or long-continued irritation. Thus, epitheliomata are 

 common in the mouth, near a rough ulcerated tooth, on the lips of pipe 

 smokers, at the edges of chronic ulcers, on the skin of workers exposed 

 to various chemical or mechanical irritants ; in cicatrices ; at the orifices 

 of the stomach and at the anus. Finally, the frequent occurrence of car- 

 cinoma of the liver with cirrhosis, though less easy of interpretation than 

 many instances of the association of tumors with chronic inflammation, 

 is worthy of notice in this connection. 



Before concluding this brief survey of the relationships of tumors to 

 trauma, prolonged irritation, and chronic inflammation, ' it may be wise 

 to remind the reader that undue significance should not be attached to 



1 For an interesting study of the relationship of trauma to malignant tumor forma- 

 tion see Brosch, Virchow's Arch., Bd. clxii., p. 32, 1900, bibliography. 



