Studils t)N Crow N CiAi.L of Plants 453 



at once the sit^niticance of Rous's research achievement, especially 

 after he read in the Jointud of Experimental Medicine what 

 seemed " ample proofs of this contention " and still more so after 

 April 4, 1912, when he heard Rous address the American Asso- 

 ciation for Cancer Research.*'-' Smith, in his address " On some 

 resemblances of Crown-gall to Human Cancer," gave his estimate 

 of the value of Rous's discovery. Further, in his introduction to his, 

 Brown, and McCulloch's bulletin 255 on " The structure and 

 development of crown gall: a plant cancer," he listed this as first 

 of three points which '" tended strongly to unsettle the crystallizing 

 belief in the nonparasitic origin of cancer." 

 In his address, he said: 



Having: found no parasite in the cancer cells, a majority of the animal 

 pathologists have given up the idea that cancer can be of parasitic origin. 

 For a generation the research workers fell back upon Cohnheim's hypo- 

 thesis that cancers were due to the development of small fragments of 

 tissue cut off from the parent layer during embryonal growth, to be 

 enclosed in other tissue and lie dormant until acted on abnormally later 

 in life by some unknown stimulus. But while studies of the animal body 

 show that such separation of small portions of tissue from the germinal 

 layer is not uncommon, research workers on cancer are now generally 

 agreed, I believe, that there are many phenomena connected with the 

 development of cancer for which this hypothesis of Cohnheim offers a 

 wholly inadequate explanation. Moreover, what induces these dormant 

 cells to develop was never determined. A very favorite theory with cancer 

 specialists has been that the cancer cell is the only parasite, and that no 

 infections could be obtained on animals unless the living cancer cell were 

 present. This hypothesis must now be abandoned owing to the discovery by 

 Peyton Rous (1911) that sarcoma of chickens may be produced in the 

 absence of cancer cells, /'. e., by cancerous fluid filtered free from all traces 

 of living cancer cells. So far as I know he has not expressed any opinion 

 as to the nature of the infection which has been separated from his ground 

 chicken sarcomata by centrifuging and also by filtration through Berkefeld 

 bougies, but in the light of the evidence we have secured from plants 

 I believe you will agree with me that it can be nothing else than a living 

 microorganism, minute enough to pass through the walls of the rather 

 coarse filter. s* 



Francis Peyton Rous, Baltimore-born and educated at Johns 

 Hopkins University and Medical School, during 1905-1906 had 

 been resident house officer of Johns Hopkins Hospital and then 



^Udem, 11. 



'* On some resemblances of crown-gall to human cancer, op. cit., reprint, 4. 



