Medicine is applied biology. Medical problems, therefore, are fundamentally biologic problems. This includes cancer, which was recognized as belonging in this sphere many years ago by a few pathologists but, curiously enough, remained with little attention on the part of biologists themselves until quite recently.
Until comparatively recently, cancer was studied mostly in its gross pathologic-anatomic aspects. Better microscopes made possible enunciation of the cell doctrine, whereupon cancer was placed in its true category of being a cellular growth and maldevelopment. Even so, few biologists, in whose fields the problems of cellular growth and development are paramount, recognized the relationship to a sufficient degree to work on it. Virchow's dictum that all cells come from preexisting cells led to a persistent search for cellular beginnings, and the literature teems with demonstrations which often were anything but conclusive as to the exact cellular origin of the various types of cancer.
A serious difficulty faced