584 Third European Journey 



in man's understanding of the greatest human malady," he was 

 given the association's annual one thousand dollar prize.^^ 



According to deRopp, the third form of plant tumors — on 

 hybrids of Nicotiana Langsdorfi and N. glauca — are of interest 

 because, to quote him, " the abnormal growth results " from a 

 cytoplasmic disturbance occasioned by the introduction of the 

 chromosome complement of N. Langsdorfi into the cytoplasm of 

 N, glauca. . . . Such tumours," deRopp says, 



develop only in hybrids in which N. Langsdorfi is used as the pollen parent. 

 The tumour tissue was cultured in vitro by White (Amer. Jour. Bot. 26: 

 59, 1939), who showed that it would continue to grow as a tumour when 

 grafted back on to normal plants. He showed also that this tumour tissue 

 was capable of differentiating organs in vitro, in which respect it differs 

 from crown-gall tissue and virus wound-tumour tissue. 



That Smith adhered to a parasitic theory of animal cancer 

 etiology seems undoubted. But what form, or the nature and 

 mode of action, of parasite or parasitic agency was stated on the 

 basis only of what authentic experimental evidence allowed. He 

 believed that " the products of parasites or symbionts [are] the 

 probable cause of most cancers or at least of their initial stages." ^^ 

 A preponderance of utterances seems to have favored a virus 

 interpretation, as yet experimentally undetermined: analogous to 

 the bacterium of tumors in plants. In practically the last working 

 years of his life, 1926, he would still be urging more research 

 on the cancer cell: " Is the stimulus to this malignant overgrowth 

 intrinsic or extrinsic? " he would ask. " Does it come from within 

 the cell, due to some change in its internal mechanism brought 

 about by a parasite or by some non-living irritant, or is it due to 

 a changed environment acting on an otherwise normal cell ? Here 

 is the problem that lies just ahead of us." ^® 



Since 1922 he had given a large share of his attention to an 

 important series of experimental tests to determine with the use 

 of the potentiometer and electrometric titration the hydrogen-ion 

 concentration and total acidity of various crown gall tumors. The 



"■^ Science 111(2871): 21, Jan. 6, 1950; abstract of Dr. Braun's paper, Thermal 

 inactivation studies on the tumor-inducing principle in crown gall, Phytopathology 

 40(1): 3, Jan. 1950. 



^* T. W. Whitaker, ]our. Arnold Arbore!u?n 15: 144, 1934. 



^^ Twen. cent, adv's in cancer research, op. cit., 316. 



^* Recent cancer research, op. cit., 246. 



