Abstract
It can be imagined that naturally occuring environmental carcinogens have existed in the human environment since long ago. For example, aflatoxin, a potent carcinogen, found recently in Brazilian peanuts suggests this. On the other hand, the incidence of hepatoma of rainbow trout in hatcheries throughout the United States, of which the cause is attributed to the artificial ration given to the fish, suggests that similar risk may occur in the human because of the increase of chemical productions, as Hueper stated.
The high incidence of cancer in an organ of a certain race should not be considered to be entirely genetic of that race. For if it had been considered so, some important social environmental factors which might have effect indirectly on the incidence would have escaped our attention and the study of cancer itself would not have made progress.
It is stressed by Poel and others that cancer is a terminal stage of normal cell proliferation under inadequate homeostatic restraint. In fact, many functional stages in the humen body have relation wtoh and effect on its abnormal progressive proliferation of normal cells. Furthermore etiology of environmental cancer is so complex that it is desirable to advance epidemiological, pathological, biochemical and molecular-biological researches further and deeper together for the better understanding of the nature of environmetal carcinogenesis. The problems of cancer of the skin, stomach, lung, bladder and breast in the human have been discussed from these viewpoints.
