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SCIENCE 



[N. S. Vol. XLIII. No. 1121 



tissues. In malignant neoplasms in man, 

 and the lower animals, why then may we 

 not assume for experimental purposes an 

 intracellular parasite capable of producing 

 sarcoma when infecting connective tissue 

 cells and other types of tumor when infect- 

 ing other tissues — each tissue presumptively 

 developing according to its own type? 

 Theoretically I can see no objection to this 

 view, and actually we have this very thing 

 occurring in crown gall. 



6. Parasites destroy cells. They do not 

 cause them to proliferate, and calling can- 

 cer a cell-symbiosis does not help matters. 

 Answer: The world progresses and new 

 knowledge modifies or supplants the old. 

 Menetrier, of Paris, without knowing any- 

 thing about our experimental work on 

 crown gall, and being very sceptical as to 

 the parasitic origin of cancer, saw clearly in 

 1908 (and so stated in his book) that there 

 was no objection theoretically to assuming 

 that in cancer there might be a parasite 

 which did not destroy cells, but continually 

 stimulated them to divide, only he said: 

 Wliat is the use of speculating, since no- 

 body has shown any concrete example? 

 This may have been true of that time, but 

 it is no longer true, since there is just such 

 a cell-parasite, or cell-symbiont, in crown 

 gall. 



7. In cancer, portions of the body grow 

 in places where they should not, having 

 come to the place by growth-extension from 

 the primary tumor or having been trans- 

 ported there by a blood stream or a lymph 

 stream. Nothing like this occurs in any 

 parasitic disease. Answer: Formerly this 

 statement corresponded to our knowledge, 

 but now it does not, because just this thing 

 occurs in the parasitic plant disease of 

 which I am speaking, viz., invasion or 

 growth-extension from a primary tumor re- 

 sulting in the occurrence of secondary 

 tumors in what previously were normal 

 parts of the plant ! 



8. Direct stimulation of cell growth by 

 a parasite is an unknown occurrence in 

 biology. In all eases in which parasites are 

 found within cells the effect is the destruc- 

 tion either of the parasite or of the cell. 

 Answer: Antiquated information. True of 

 many things, but not of all. Theoretically 

 a third possibility exists, and actually we 

 have it in crown gall. Here the parasitized 

 cells are not destroyed, neither are all of 

 the bacteria within them killed, but only 

 most of them. There is a very delicate bal- 

 ance between the two, which results not 

 in death of the host cells, but in an increased 

 tendency to cell-division, a tendency strong 

 enough to overcome the physiological con- 

 trol of the plant. When death results it is 

 not due to the direct action of the bacteria, 

 but to other factors, e. g., nutritional de- 

 fects, and secondary parasitisms. 



9. Since cell proliferation in tumors is 

 similar to cell proliferation under normal 

 conditions, the assumption of a parasite to 

 explain it is quite unnecessary, and makes 

 an explanation of tumor-growth more diffi- 

 cult. Answer: Similar is not necessarily 

 the same. Conclusions drawn from cul- 

 tures in vitro do not necessarily apply to 

 growth within the body. Cell-proliferation 

 of tumor tissues in the body is similar, of 

 course, to normal cell proliferation, hut 

 with a difference, namely, in the tumor 

 there is an unknoivn something, which com- 

 pels these cells to proliferate in opposition 

 to the needs of the body and in spite of the 

 physiological body control. Surely some- 

 thing very foreign to the body is required 

 to explain the undifferentiation, anaplasia 

 we call it, following von Hansemann, and 

 the excessive vegetative force of the cancer 

 cells. Moreover, so far as it is able to do so, 

 the body treats individual cancer cells, or 

 groups of cancer cells (metastatic frag- 

 ments) exactly like parasites, that is, it 

 envelops them in a blood clot and destroys 

 them. In cancer, therefore, considering 



