498 Second European Journey 



that is, Baclerjum savastanoi (the cause of olive tubercle) and Bad. beticola 

 (the cause of beet tubercle) — are negligible so far as the purposes of this 

 paper are concerned, because I regard the tumors they produce as granu- 

 lomas, not neoplasms. In fact, thus far in seeking for the physical-chemical 

 origin of neoplasms I have sought only for answers to the following 

 questions: 



(1) What are the products of the bacterial metabolism of Bact. tume- 

 jaciens . . . ? 



(2) Are any of these products capable of inducing cell proliferation 

 when injected into the growing plant? 



(3) If so, is this substance a sufficiently common product of other 

 bacterial and nonbacterial tumor-producing parasites so that it may be 

 regarded hypothetically as produced by all of them and consequently as 

 the exciting cause of all bacterial, fungus, nematode, cynipid, and other 

 vegetable galls, or must we suppose that various chemical growth excitants 

 exist? 



(4) And finally to what extent can these facts be supposed to apply to 

 human and animal neoplasms ? 



His answers or hypotheses were drawn from a wide range of 

 experiments and included comments on plant diseases " of undeter- 

 mined origin but suspected of being due to parasites " (p. 183) 

 such as curly top of sugar beet, mosaic of tobacco, and other dis- 

 eases today attributed to viruses. At one point in his paper he 

 said that his recent experiments with crown gall teratoids had led 

 him to " believe that not only the origin of fasciations but also of 

 many other duplications is to be sought in local and feeble infec- 

 tions by a variety of deep-seated microorganisms" (p. 181). 



While the origin and growth of tumors, benign or malignant, 

 was regarded by Smith as more than a chemical phenomenon, 

 he detailed many experiments making use of chemicals to trace 

 the sources of tumor inducement and growth. Especially was this 

 so when describing his experiments made to ascertain the nature 

 of the action and changes wrought in plants by chemical by- 

 products of the bacterial metabolism of Bacterium tumefaciens. 

 Experiments were made with and without the use of the crown 

 gall organism, sometimes only with the use of chemicals to study 

 the phenomena. But the mechanism of tumor formation and 

 growth was found, amid the complex of causes and conditions, 

 to be fundamentally osmotic rather than chemical. Local osmotic 

 pressure was believed to be the beginning of all tumor growth 

 (p. 175). Cell proliferation is caused by something more than 



