CANCER RESEARCH 33 



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 sys- 

 tem 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 some- 

 times 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 fre- 

 quently 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 irrita- 

 tion as a result of insufficient liquefaction of the intaken food, may also 

 be followed by cancer. Irritation caused by the consumption of alco- 

 holic 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 gall- 

 bladder is more common in women, because women more than men are, 

 as a result of certain habits, prone to suffer from gallstones, and gall- 

 stones cause a condition of constant irritation in the gallbladder. Car- 

 cinoma 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 con- 

 nection with an incarcerated stone. In the respiratory tract cancer in 



vol. lxxxvi. — 3. 



