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SCIENCE 



[N. S. Vol. XLHI. No. 1105 



(Bernhard Fischer and others) and ether 

 (Reinke) are substances that under cer- 

 tain conditions seem to exert a stimtdating 

 effect. 



6. Chemical and mechanical factors pro- 

 duce with the aid of a large quantity of 

 internal factors, or in certain cases appar- 

 ently without such aid, an increase in cell 

 proliferation that persists after the stimuli 

 have ceased, which is permanent, potentially 

 of unlimited duration in contradistinction 

 to the temporary reactions mentioned above. 

 This is the cancerous reaction with which 

 all or at least the large majority of the 

 mammalian tissues may respond. Neither 

 potential immortality — some, or perhaps 

 all, somatic cells are potentially immortal 

 — nor the power of continued proliferation, 

 which in all probability even certain ordi- 

 nary somatic cells possess, is characteristic 

 of this reaction, but rather the increase in 

 proliferative power, and furthermore the 

 permanency of the reaction in response to a 

 temporary, non-permanent stimulus. We 

 have then to assume that a labile cell-system 

 which responds to temporary stimuli with a 

 temporary reaction is transformed under 

 the influence of certain stimuli, and often 

 with the aid of hereditary factors, into a 

 . stable system which shows a greater prolif- 

 erative power than the labile system. The 

 stimulus thus brings about merely a trans- 

 fonnation of the cells into a new kind of 

 ceU-system, which proliferates indefinitely 

 at a more or less increased rate. Such a 

 transformation may be called a mutation.^ 

 Inasmuch as all, or the large majority of 

 all body cells are liable to this change, they 

 must have from the beginning in their or- 

 ganization a mechanism that provides for 

 the possibility of such a mutation. 



3 We would have to deal in this case with a mu- 

 tation, not in a germ cell, but in a somatic cell. 

 For a more detailed discussion of this problem cf. 

 Leo Iioeb, "Germ Cells and Somatic Cells," Amer- 

 ican Naturalist, Vol. 49, 1915, p. 286. 



According to this conception, we must 

 then assume that all or most cells have po- 

 tentially two equilibria, the normal one 

 and the cancerous ; they begin life with the 

 normal equilibrium, but under the influence 

 of certain stimuli, with or without the co- 

 operation of hereditary factors, they are 

 transferred to the cancerous equilibrium. 



Cells in the normal equilibrium react to 

 stimuli in the manner indicated above 

 (types 1 to 5) ; ultimately they return in- 

 variably to the normal equilibrium after 

 the stimulus has ceased to act. Cancerous 

 cells, on the other hand, may perhaps be 

 exterminated, but they are not known to 

 return to the normal equilibrium. 



There is, however, an alternative to this 

 conception which would eliminate the ne- 

 cessity for assuming a new equilibrium for 

 cancerous proliferation, an assumption for 

 which naturally no analogy can exist. If 

 we assume that an external agent associated 

 with the cell, rather than a physico-chem- 

 ical mechanism within the cell, produces 

 the cancerous proliferation, the latter would 

 no longer represent a unique condition, but 

 would be a special application of one of the 

 types 3 to 5, in which, however, the stim- 

 ulus would act incessantly. Such a stim- 

 ulus could be supplied through multiplying 

 microorganisms which essentially represent 

 constantly newly formed external chemical 

 stimuli. Such microorganisms would not 

 be identical with bacteria causing various 

 ordinary infectious diseases. As we have 

 shown at an early stage of our investiga- 

 tions, cancer among animals is not infec- 

 tious in the sense in which certain other dis- 

 eases are infectious. "We could feed tumor 

 tissue to normal animals or keep normal 

 animals in the same cage with cancerous 

 animals without a transfer of the disease 

 taking place ; neither could Ehrlich produce 

 cancer in young mice which were suckled 

 by cancerous animals. But this does not 



