436 First European Journey 



Things not yet determined are the number of strains, the extent of cross 

 inoculabihty, the cause of resistance, the reason for loss of virulence on 

 media, the nature of certain beet tumors and the question whether right 

 looking but non-infectious colonies from such tumors and occasionally from 

 other tumors are really the parasite deprived of infectious powers by sojourn 

 in the plant under unfavorable conditions or are only deceiving sapro- 

 phytes, extent of variability of the organism on culture media and in the 

 tumor, production of metastasizing tumors in animals, etc. 



Smith would spend many years trying " to think out the rationale 

 of what goes on in the cell following the introduction of the 

 crowngall organism. What we see is excessive and abnormal multi- 

 plication of the tissues resulting in a tumor, a hyperplasia," he 

 would say ^^ in 1917. "What we would wish to know is the 

 mechanism of the growth— that is, the chemical or physical 

 stimulus behind the observed phenomena — since, if we can com- 

 prehend it in the plant, we may be able to apply our knowledge 

 to the understanding of similar phenomena in man and animals." 



He admitted that at first he thought of " the crowngall pheno- 

 mena as much more complex than it really is. . . . In the beginning 

 I had," he wrote, 



what I now believe to be a wrong conception of growth. I looked upon it 

 as something that an outside substance could directly stimulate into develop- 

 ment, but probably it is not that (Weigert, Ribbert, Loeb) . Growth is the 

 normal function of cells. They are always multiplying when they are not 

 inhibited by one thing or another. Growth, then, if this view is correct, 

 comes about not by the direct application of stimuli, but indirectly by the 

 removal of various inhibitions. ... In crowngalls the removal of growth 

 inhibitions is brought about, I think, by the physical action of substances 

 liberated within the tumor cells as the result of the metabolism of the 

 imprisoned bacteria. 



From that time his use of the word " stimulus " was to be con- 

 strued as " the remover of an inhibition." 



He became a student of plant tumors and their etiology. He 

 found indicated analogies in structure and function between the 

 higher plants and animals in health and disease.*^*' He approached 

 his comparison between crown gall and sarcoma with " mental 

 reservations." He was more confident of his analogy between 

 crown gall and " a nontypical epithelioma or carcinoma." *'^ Crown 



'^" Mechanism of tumor growth in crowngall, Jour. Agric. Res. 8: 165-167. 

 *" The structure and development of crown gall, analogies, op. cit., 53-57. 

 "^Idein, 54. 



