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��TEE SCIENTIFIC INVESTIGATION OF CANCER 217
cancerous transformation produces an endless increase in cell prolifera- tion. In most cases cancer cells as well as normal cells are^ as far as we can determine now, potentially immortal, which means that, given proper conditions for existence, they can live indefinitely and survive indefinitely the organism of which at one time they formed a part. Certaui normal tissues may also not only live indefinitely, but also grow indefinitely, and cancerous cells differ from normal cells merely in their excessive proliferative function and in their greater power to attack the deeper tissues. This surplus power has been attained under the influence of the external stimuli which we mentioned before, with or without the cooperation of the internal factors.
The essential problem then is : How does it come about that under certain conditions stimuli which apparently are only temporary lead to changes which continue indefinitely after the stimulus has ceased to act? We must assume then that the organization of the cell has changed from one equilibrium — that of the normal cell — ^to another, which latter is characterized by greater proliferative activity and a greater power to penetrate into deeper tissues. The organization of some cells has been changed imder the influence of growth stimuli and they are now somehow machines of a different character, which react differ- ently to external factors. We might call such a transformation a muta- tion, and we have analogies for such a change in similar transforma- tions which may suddenly occur in germ cells and lead to the produc- tion of new varieties and species. We have also in the case of ordinary tissue cells (in contradistinction to germ cells) some evidences that certain changes induced by external factors may be transmitted at least in some degree to succeeding generations of ordinary tissue cells. This is true of tissue cells as well as of germ cells; for tissue cells are potentially similarly affected as cancer cells. It is obvious then that one explanarf;ion for the origin of cancer may be the following. All or almost all normal cells possess two equilibria: (1) the equilibrium which is manifested under ordinary conditions, in which the cell has a limited proliferative power and (2) an equilibrium in which the cell has a greater proliferative power. A normal cell which has been changed from the first to the second equilibrium we call a cfincer cell.
There is, however, another alternative in explaining the cancerous transformation, which would in certain respects furnish a simpler expla- nation., If we assume that in addition to the conditions which are im- portant for the origin of cancer (namely, the internal and external factors before mentioned), there is hidden a constantly acting stimulus within the tumor, then the reaction of the tumor cell would be essen- tially similar to that of any normal cell. The tumor cell would react constantly through an increased proliferative activity merely as a reevlt of an eternally acting stimulus. Such a continuous active stimu-
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