THE PARASITIC THEORY OF NEW GROWTHS 277 



being directed aright ? Are the arguments employed in support 

 of this theory of the infectious origin of malignant neoplasms 

 thoroughly sound ? Do the almost innumerable observations 

 which have been made during the last few years bear out the 

 assumption, or have we been neglecting other important factors 

 in the etiology of new growths in the keenness of our desire to 

 determine some specific causative agent ? 



These are the matters I wish to discuss. The time, indeed, 

 is opportune for such discussion when of late, upon this side of 

 the ocean, two well-known surgeons like Roswell Park of Buffalo * 

 and Collins Warren of Boston 2 have placed themselves in evidence 

 as favouring the theory of infectious origin, and when, on the 

 other side, a Cancer Number of that well-known journal, the 

 Practitioner? with its series of articles by responsible writers deal- 

 ing with different phases of the subject, most assuredly leads up 

 to the conclusion that cancer is an infectious disease. 



The Parasitic Theory 



It will be well, in the first place, to adduce the main argu- 

 ments in favour of the parasitic origin and infectious nature of 

 malignant growths. These, stated briefly and impartially, are 

 the following : 



1. That the increase in frequency in malignant tumours in 

 civilized communities during the last four decades is wholly out 

 of proportion to the possible action of any factor, save the 

 gradual spread of some infective agent. It is in excess of any 

 lessening of the death-rate, and not to be accounted for merely 

 by the increased longevity of civilized races — is not, that is, to 

 be explained by the fact that a larger number of individuals 

 now reach the cancer age. The increase is to be seen in country 

 as well as in urban districts, in European as well as in American 

 communities, and cannot therefore be attributed to any one 

 alteration in the mode of fife, to altered habits, altered environ- 

 ment. There is no other common factor capable of explaining the 

 increase, hence, per exclusionem, we must fall back upon infection. 



2. That the incidence of the disease is frequently found to 

 be peculiarly localized — certain districts, mainly low-lying, are 



1 Roswell Park, Trans. Amer. Surg. Assoc, xvi., 1808, p. 182. 



8 Collins Warren, Boston Med. and Surg. Journ. vol. cxliii., 1900, p. 25. 



* Practitioner, Cancer Number, April 1899. 



