FURTHl^R RliSHARCmiS IN DiSHASI-S OF Fl.ANTS 535 



m.'.lignancics, and if so, the rationale indicated a parasite in cancer, 

 an ori^anism with capacities for adaptation and reproduction, and 

 possibly other descnbable characters. Observe, however, his sug- 

 gestions as to the nature of this possible, discoverable organism 

 or carcinogenic agent invariably were drawn from his knowledge 

 of plant diseases or from those human and animal diseases in 

 which a known parasitic microorganism was the cause. 



Unyielding search in tuberculosis, leprosy, syphilis, malaria, 

 yellow fever, and other diseases had ended each time in finally 

 isolating the real causal parasite or had brought the final isolation 

 closer. This argifed that experimental scientists dared not yield 

 in their relentless search for a parasite in cancer. Especially was 

 this so, since it had been shown that cancer in animals can be 

 caused by parasites, Gongylouenia neoplasticuvi (Fibiger), Cys- 

 ticercus fasciolaris (Borrel) and by viruses — Rous's (and James 

 Murphy et al.) chicken sarcoma and Akira Fujinami's indepen- 

 dently discovered fowl myxosarcoma, which was tantamount to a 

 verification of Rous's work. To these have been since added, 

 among others, the Shope rabbit papilloma, Lucke frog kidney 

 carcinoma, Bittner mouse breast cancer, and Yoshida rat ascites 

 sarcoma.^'* 



Smith never maintained at all points completeness of analogy 

 betu'een crown gall of plants and human and animal cancers. 

 Yet, he insisted, studies of the genetic origin and environmental 

 development of tumors were made possible by comparatively 

 studying malignant and non-parasitic tumors in plants. Since the 

 causal organism of malignant plant tumors had been isolated, 

 it followed, however slight the presumption, that a parasitic 

 organism causing malignancies in animals and man might also 

 be found — not the same organism but one with similar capabili- 

 ties. At least, clues or leads helpful to ultimate discoveries or 

 solution were available through the study of plant tumors. 



Under controlled conditions, he examined the processes of 

 tumor formation and growth, the chemico-physical stimuli which 

 induce cell division and multiplication, and the nature of malig- 

 nant in contrast to benign growths. To determine the nature of 

 chemical substances liberated in tissues by parasites to cause plant 



^* Science 110(2844): 20, July 1, 1949 (review by Kanem.itsu Sugiura of Caitcer: 

 radiations, virus, environment, vol. II, by Dr. J. Maisin). 



