The insidious onset of a malignant tumor with the lack of positive evidence, in the majority of instances, until the case is far advanced, is perhaps the greatest difficulty in the way of a decided reduction in cancer mortality. Certain well established facts of cancer etiology may be briefly stated in order to explain the basis of the experiments of which this paper constitutes a preliminary report.
Broadly speaking, the development of malignant tumors rather frequently follows irritation, though no irritant is specific. It is generally accepted that not every one exposed to the action of any given irritant develops a tumor. In other words, there is an apparent predisposition as well as an actual inciting irritant. Again, broadly speaking, since exact statements are not possible in the present state of our knowledge, this predisposition becomes more evident at a certain period in life, a period spoken of as the