SLIGHTLY more than 5 per cent of all malignant lesions occur in the colon, and the majority of these are located in the terminal four and one-half inches and within reach of the examining finger. This type of carcinoma occurs most often between the ages of 40 and 70 years, but cases have been known to occur as early as at the age of 10 years. The preponderant occurrence of neoplasms at points of fixation in the colon strongly suggests that irritation is a major causative factor. However, no definite predisposition can be proven except in cases arising from multiple polyposis in which it must be assumed that an abnormality previously existed at the site of the polyp formation. As yet no satisfactory evidence has been adduced that carcinoma develops in tissues altered by the presence of hemorrhoids, fistulae, or cicatrices. Clinically, three types of growth are encountered: 1. The polypoid or protuberant growth, which is movable and ulcerates superficially. 2. The flat crater-like excavated growth with indur...