202 THE SCIENTIFIC MONTHLY
large extent the behavior of the fundamental factors influencing his internal environment. As we attempt, however, to analyze the im- portant hereditary factors, we are in man faced with certain limiting facts. Inadequate methods of observation, diagnosis and recording; magnified effects of environment due to a long life cycle; small num- bers of young, and a deliberate system of out-breeding which com- pletely mixes and confuses the material with which we have to deal, force us to the conclusion that studies of hereditarj' tendencies to can- cer in man as they are at present carried on, will yield little, if any- thing, of value to the subject under consideration. We may further say that present indications are that genetic studies with lower mam- mals, while having proved definitely the existence of hereditary tend- encies to cancer, indicate that a complex type of inheritance is involved which could at best be of negligible importance as a practical preven- tive or protective measure in man.
This may give the erroneous impression that genetic studies even with lower animals are superfludus in the field of cancer research. This would be most unfortunate, however, for it appears certain that the etiology of cancer is a problem of growth and differentiation and as fiuch is essentially biological in nature. It may therefore be approached perhaps with marked success, through genetic investigations with rap- idly breeding small mammals in which a study of the biological factors fundamentally important can, under proper circumstances, be best Accomplished.
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