874 



SCIENCE 



[N. S. Vol. XLIII. No. 1121 



visible they are called metastatic (or shift- 

 ing) growths. Some modern writers, how- 

 ever, use the word metastasis for a daughter 

 tumor of any origin. 



As I have said, nothing is known respect- 

 ing the cause of these human tumors and 

 the great majority of cancer workers have 

 come to the conclusion (which I believe is 

 erroneous) that they can not be due to 

 parasites. 



It is well here to pass in review some of 

 the objections to a parasitic theory of can- 

 cer: (1) Because many authors of distin- 

 guished reputation (Ribbert, for example) 

 maintain that they are insuperable; (2) be- 

 cause so long as they are not met various 

 persons will be discouraged from under- 

 taking active researches designed to un- 

 cover the parasite; and (3) because, finally, 

 if I can convince you that crown gall is a 

 cancer, you will then be ready to admit that 

 what requires a schizomycete for its pro- 

 duction in the plant is not likely to be pro- 

 duced in any very different way in man 

 and animals. Here then are some of the 

 objections, and I will meet them as fairly 

 as I can. 



1. Nothing definite in the way of a para- 

 site has been made out by use of the micro- 

 scope. Answer: This is admitted, but it 

 proves nothing. If we exclude the Negri 

 bodies, still in dispute, the same is true for 

 rabies. And in cancer we have the Plimmer 

 bodies and other cell-inclusions of a doubt- 

 ful nature, some of which may be bacterial 

 or protozoan. The etiology of crown gall 

 would still be in doubt if we had depended 

 solely on the microscope, for no ordinary 

 staining will demonstrate a bacterium in 

 the cells, and yet it is there. For the final 

 analysis recourse must be had to cultures 

 and inoculations. There are then some 

 problems in pathology which never can be 

 solved simply by the use of the microscope. 



2. From cancer no parasite has been iso- 



lated in spite of diligent bacteriological 

 search. Innumerable cultures have been 

 made and many inoculations and all have 

 failed. Ansiver: The same is true of yellow 

 fever. No parasite has been found. Until 

 recently the same was true of syphilis. Ten 

 years ago it was true of crown gall. There 

 may be some very special reason (as in 

 crown gall, or in certain types of arthritis) 

 why isolations have failed; or the right 

 organism may have been isolated and inocu- 

 lations may have failed simply because the 

 inoculated animals were normal, i. e., fully 

 protected by their leucocytes and therefore 

 not susceptible. We must, I think, con- 

 ceive of cancer as developing only in a 

 weakened, unprotected condition of the 

 body. The more or less ready growth of 

 grafted cancer in certain animals offers no 

 real contradiction because here the condi- 

 tions are somewhat different from what 

 they would be in case of a naked bacterial 

 inoculation, because the grafted cancer cells 

 are autochthonous cells and are introduced 

 into the mouse or other experimental ani- 

 mal in a considerable compact mass, the 

 inner cells shielded by the outer ones and 

 all developing a kind of protective aura 

 under the influence of which union with 

 the host tissues takes place and the cancer- 

 ous growth continues. 



3. Heredity is a sufficient explanation. 

 Answer: The same thing was said repeat- 

 edly of tuberculosis prior to 1884. Now we 

 see that heredity furnished the canvas but 

 could not paint the picture. Miss Maude 

 Slye's work on heredity of cancer in mice 

 is astonishing and praiseworthy, but I do not 

 feel sure that a similar picture could not be 

 obtained by breeding together tuberculous 

 animals, indeed I am quite certain that the 

 results of such experiments would be a 

 vastly increased number of tubercular ani- 

 mals, and if we knew no more about the 

 cause of tuberculosis than we do about the 



