More recent scientific study has attempted to show that cancer originates from what are called “_embryonic rests_,” or pre-natal, wrongly placed, tissue elements, which at some time or other take on morbid action and develop into what we know as the various forms of cancer. Williams says, “From a biological standpoint tumor formation must be regarded as a phenomenon of the same order as reproduction in general: that is to say, as a special form of overgrowth of the individual.” But here again it is necessary to determine what causes them at certain times and in certain places to thus proliferate and form new tissue, which then becomes malignant and may proceed to destroy all contiguous tissues, and even to cause death. _Traumatism_ has been claimed by many as the cause which determines the activity of the misplaced cells, and starts them on their disastrous or rampant course: the various percentages of the cases in which it was believed that traumatism started up the malignant process has varied greatly with different observers, even up to 50 per cent, or more. But it is far from proven that this is always the case, nor does local injury in any way explain the persistency with which malignant disease, when once started, pursues its destructive and even fatal career; nor can traumatism account for the great tendency to recurrence constantly observed, either in the former site or at some distant focus, through the agency of the lymphatic or vascular system. For of multitudinous traumatisms, even in cancer subjects, how few ever develop into malignant disease! It would seem, therefore, that for the development of the local manifestation of cancer (the tumor or new growth) three elements are requisite, namely: 1. A predisposition or suitable blood condition. 2. A local stimulation or irritation of the part affected, _upon_, 3. The site of an “embryonic rest.” On the basis of the embryonic theory surgeons have of late most earnestly advocated the very early and complete removal of malignant lesions, including those of suspected malignancy, and even also the removal of many innocent lesions which are observed occasionally to lead to cancerous formation; and unless a better plan can be determined this cannot be urged too strongly in proper cases.