in cancer, let us now briefly survey the typical cancers of old age. Such a review will demonstrate that for the production of the majority of all cancers the long-continued action of external stimuli is of the greatest importance. We stated that in civilized countries the large majority of human cancers occur in the alimentary and female generative organs, while the respiratory tract and kidney and ureter and the nervous system are much more rarely affected. The alimentary tract is the one through which the solid substances pass and which is therefore most easily exposed to constant irritation and possibly the action of certain parasites while through the respiratory and excretory tract (kidney, ureter) only gaseous substances or liquids pass; there is here therefore much less opportunity for long-continued irritation, and consequently less cancer. In the alimentary tract, those parts in which mainly fluid material is present, namely the small intestines, are least affected, while those in which especially solid material stagnates as in the stomach and rectum, cancer is most frequent. Cancer of the lip is frequently caused through the irritation of a pipe, cancer of the tongue and cheek is sometimes the result of constant irritation on the part of a defective tooth or prothesis. In the esophagus those places are the favorite seats where there is the greatest opportunity for irritation; in the stomach cancer is frequently found at the same site where gastric ulcer occurs most frequently and where the foodstuffs are apt to press against the pylorus in entering the small intestines. Certain chronic digestive disturbances characterized by a decrease or lack of digestive substances secreted by the stomach (achylia gastrica), in which there is therefore more irritation as a result of insufficient liquefaction of the intaken food, may also be followed by cancer. Irritation caused by the consumption of alcoholic beverages seems, in certain countries in which cancer of the stomach is more frequent in men than in women, to be one of the causes of gastric carcinoma. In the intestines cancer is frequently preceded by the formation of papillomata which again are in most cases the result of chronic irritation and inflammatory processes. Cancer of the gallbladder is more common in women, because women more than men are, as a result of certain habits, prone to suffer from gallstones, and gallstones cause a condition of constant irritation in the gallbladder. Carcinoma in the bile ducts has been observed to originate at a place where a gallstone was most likely to find obstruction in its passage into the intestines.
In the female generative organs cancer is most frequent in the cervix of the uterus, where, as the result of preceding labors, and of infection, tears and chronic inflammatory conditions are found to occur. In the mammary gland also cancer stands often in causal relation to preceding inflammatory conditions. In the ureter cancer has been found in connection with an incarcerated stone. In the respiratory tract cancer in
