226 THE SCIENTIFIC MONTHLY
which is essentially the problem of general biology, is broadened and deepened through cancer research. Cancer research is, in fact, a depart- ment of comparative general biology, and its fate is closely bound up with that of other biological sciences.
In closing I shall say a few words in regard to the practical appli- cation of cancer research — the prevention and treatment of the disease. We have found that there are internal and external factors concerned in the origin of cancer. Of the internal factors, heredity and the presence of certain malformations play a very prominent part in the development of cancer, unquestionably in animals and probably also in man. Of the external factors long-continued stimulation, long-con- tinued irritation, of tit^sues is one of the important causative conditions. If we wish to prevent cancer we must be able to control all these factors. It is comparatively easy to do this in the case of external factors. Long- continued irritation of anv sort must be avoided. Under certain con- ditions, for instance, it might be wise to remove all pigmented moles which are exposed to irritation. The control of the factor of heredity is more difficult. It would be one of the problems of eugenics. The difficulty, however, in applying theoretical knowledge in this field is two-fold: in the first place, living organisms are a great complex of hereditary unit factors, which are transferred from generation to gen- eration independently of one another. This makes a selective mating very difficult. Advantageous factors are combined in the same organism with inferior ones, and it is at present almost impossible — at least in most cases — to determine which factors merit greater consideration, especially when we consider that the large majority of hereditary unit factors in the case of the higher organisms are almost unknown to us. The second difficulty in practical eugenics is the danger that methods which might be suggested for certain purposes would be contrary to that social understanding and sympathy which is the basal factor of our civilization. All we can say at present is that it might be advis- able to avoid interbreeding between strains in both of which the tend- ency to cancer is dominant. But in the case of man even this con- clusion can, at the present time, be drawn in only a tentative way.
As to the treatment : Science shows us that cancer starts as a local disturbance, and, from what we have learned, it follows that the earlier the local growth is completely eradicated the better will be the results. For this eradication surgical means should be employed in the large majority of cases. In a few selected cases some other methods might be indicated. Certain methods, depending on the application of differ- ent principles, are at present still of an entirely experimental character. How far it will be possible to develop them in the future we are not able to foretell. The investigator must follow his path quietly, guided by purely scientific aims. This will be the surest method of bringing about the greatest practical results.
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