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SCIENCE 



[N. 8. Vol. XLIII. No. ;i05 



malian tumors. "We would have to assume 

 the existence of different substances of this 

 kind, and different substances always call 

 forth a specific activity of connective tissue 

 cells resulting in the reproduction of the 

 original kind of tumor, and stimulating 

 endlessly the production of the same specific 

 substance within the fibroblasts. Just as in 

 the case of the corpus luteum substance 

 which is responsible for the production of 

 deciduomata, the cooperation of a mechan- 

 ical factor seems to be essential for the 

 stimulation of tumor growth in fowl. "We 

 would most probably have to give this inter- 

 pretation to these phenomena if the obser- 

 vation of Casimir Funk, according to whom 

 an alcoholic extract of the tumor contains 

 the active agent, could be confirmed in a 

 larger number of cases. If this should 

 prove correct, we may expect to find corre- 

 sponding conditions in mammalian cancer. 

 A study of heredity in cancer of the fowl 

 would close this chain of investigations, 

 and with the analysis of internal and ex- 

 ternal factors in cancer already on a solid 

 foundation, we could then conclude that 

 the causes of cancer in their main outline 

 have been satisfactorily analyzed. Of 

 course underneath this first plane of causes 

 there are connections which extend further 

 into fields where they meet with other 

 factors determining cell and tissue life in 

 its dependence upon physical and chemical 

 laws, and thus we are led into deeper planes 

 of causation. But here the problems have 

 become identical with those of general biol- 

 ogy, the laws governing cell division and 

 ameboid movements in cancer cells not 

 differing from those of other cells. 



In this connection a few words concern- 

 ing the definition of cancer might not be out 

 of place. It might indeed be assumed that 

 a definition of cancer satisfying past and 

 future research is one of the essential re- 

 quirements for the fruitful pursuit of in- 



vestigation. On the contrary, I believe that 

 at the present stage of investigation prog- 

 ress may be retarded through premature 

 rigidity in defining cancer, and especially 

 through insisting on the proof that second- 

 ary tumors originate from transplanted 

 cells. In the case of sarcoma of the rat and 

 mouse, this proof has so far been supplied 

 only in the rat sarcoma of the thyroid found 

 in Chicago, and is merely based on analogy 

 in the case of the large majority of other 

 sarcomata. Since it has now been shown 

 that in sarcoma of fowl an agent associated 

 with the tumor, but separable from it, may 

 just as well give origin to new growths, we 

 may well hesitate in excluding from con- 

 sideration new formations which in all prob- 

 ability under certain conditions have their 

 origin in transplanted cells, while in other 

 cases they may perhaps be propagated 

 through an agent associated with the tumor. 

 I refer here especially to the so-called 

 lympho-sareoma or small round cell sar- 

 coma of dogs which, after transplantation 

 in dogs, apparently grows from the trans- 

 planted cells (Sticker, Ewing and Beebe, 

 and L. Loeb), while in the fox, according 

 to von Dungern, the tumor cells are com- 

 posed of host tissue. May we not, in case 

 von Dungern 's view should prove correct, 

 have to consider the possibility that the 

 transplanted dog cells perished in the for- 

 eign species, and that the associated agent 

 stimulated the host cells to proliferation ? 



With the factors which we have already 

 analyzed — factors of heredity, of internal 

 secretion, of external, chemical and mechan- 

 ical stimulation — we are in a position to 

 control to a great extent the cancer rate in 

 certain species of animals. As we said, we 

 can not yet exclude with certainty the 

 other alternative, namely, microorganisms, 

 as an additional causative factor. 



After so many futile attempts to estab- 

 lish a direct proof of their presence, further 



