SYMPOSIUM ON PUBLIC HEALTH. PROBLEMS 99 
literature has developed about this marvelous scientific enigma. 
The theory most generally accepted at the present time is that 
most malignant growths have as the exciting cause of their 
development some form of irritation. There are many curious 
and apparently significant facts lending strength to this theory. 
As an illustration of this eighty-five per cent of the cancers of 
the lip develop in smokers. Fifty per cent of the cancers of the 
stomach are found developing from the edge of a previous 
ulcer. Dr. Fibiger, of Denmark, noticed that the native rats 
that died around the sugar warehouses of that country never 
had cancer of stomach or intestines; while the rats that came 
over in the ships from America and died, frequently 
had cancer of the stomach or intestines. In looking 
about for the explanation, he discovered that the American rats 
often ate American cockroaches. He then imported some of 
these cockroaches from America and fed them to the Danish 
rats, with the result that these rats also developed cancer of 
the stomach and intestines. This led to the further investiga- 
tion of the cockroaches found in America, which disclosed 
that they frequently harbored a small parasitic worm which 
was not found in Danish roaches. The irritation caused by the 
intestinal worms undoubtedly was the explanation of the fre- 
quent presence of malignancy in the intestinal tube of the 
American rodents. Many more instances could be cited where 
the development of malignancy seems to be coincident with the 
production of a chronic irritation. Cancer of the kidney is one 
of these where presence of stone in fifty per cent of the cases 
probably accounts for presence of cancer. In eighty-five per 
cent of the cases of cancer of the gall bladder, gall stones are 
found. Cancer of the groin is very common in chimney 
sweeps, and in sailors. In the first-named the soot, together 
with the loop of rope in which they swing, produces the 
necessary irritation and this is found, i.e., the irritation from 
the rope, true also of the sailors. In Kashmir, a province of 
India, the natives carry a charcoal stove under their cloaks 
and against the skin of the abdomen to ward off the cold. The 
most frequent form of cancer, therefore, in this region of the 
world is that of the skin of the abdomen. In China cancer of 
the pharnyx is very common among the male portion of the 
population, while it is almost unknown among the women. 
The explanation is that the men eat at the first table at meal 
