FURTHl-R RliSHARCHHS IN DlSllASES OF PLANTS 563 



normally changed that they will go on indclinitLly "" growing and 

 multiplying without the primary cause subsisting."' 



In 192"^, at the eighteenth meeting of the American Association 

 for Cancer Research, Dr. Hwing would ask him whether he main- 

 tained that a parasitic organism exists in connection with those 

 experimental cancers produced by repeated coal tar paintings, a 

 subject wc shall discuss further very soon. Dr. Ewing would ask 

 Dr. Smith, " Does the microorganism get in with the tar? ... Or 

 are we required to assume that there are a great many factors in 

 the production of cancer? " Dr. Smith would reply: 



Direct irritation certainly cannot be the cause of tar-cancer. It remains 

 to be explained why some spots of the painted area respond while most 

 do not. We do not know just how chemical substances act on the cells to 

 produce a malii^nant process, and whether a parasite is necessary after the 

 change once occurs for it to go on. It may be that several types of chemical 

 stimulus will give the same result, and that we might have cells so abnor- 

 mally changed that they will go on indefinitely without the primary cause 

 continuing to act. 



Since his earliest publications on crown gall, Smith had believed 

 that the bacteria were located intracellularly. In bulletin 255, 

 " The structure and development of crown gall: a plant cancer," ®^ 

 he had pronounced the situs of the bacteria " must occur within 

 the cells," since the microscope did not show their occurrence 

 between the cells or in the vessels. Because of the proof that 

 bacteria had been found in the tumor, this conclusion had seemed 

 to him inescapable unless the causal organism was to be supposed 

 as " ultramicroscopic, i. e., totally unlike their form on culture- 

 media, and also unlike the rods and Y-shaped bodies that diffuse 

 out of the sections. Then, of course," he said, " they might occur 

 anywhere." In 1911 his belief was that the stimulus of the 

 mechanism of the controlling cell division came from within the 

 cell, and in a footnote he had said: '°'' " It is inconceivable to the 

 writer that a foreign organism, by any localized and brief presence 

 in the tissues, should so modify cell inheritance that, after the 

 organism and its products have disappeared, the cells should 

 continue to develop abnormally rather than return to their normal 

 habit." No later than 1922 he confessed as to crown gall " an 



"/o«r. Cancer Research 9: 497, 1925. 



"O/^ r//., 17. '■"Udem, fn. 1. 



