94 J. B. CLELAND. 
greater, ceteris paribus, will be the occurrence of cancer 
amongst them. Probably this very fact, that more people 
through increased medical skill and better public health 
protection reach old age than formerly, and thereby in- 
crease the average span of life of the population, accounts 
in some measure for the apparent increase of cancer. 
The third factor, exposure to certain forms of chronic 
wrritation, is an important one. In man we know that such 
factors may consist in irritation of the lip from a clay or 
other pipe, injury to the tongue from a jagged tooth, un- 
wise exposure of the operator to X-rays, irritation of the 
serotum from soot in chimney sweeps, frequent burns on 
the chest from braziers containing hot charcoal in certain 
inhabitants of India, etc. In Epimys norvegicus we have 
the irritation of the stomach caused by a round worm, 
Gongylonema neoplasticum. In cattle in Australia we have 
squamous epithelioma of the orbital region, probably due to 
the chronic irritation of grass seeds or other foreign bodies, 
and the same condition occurring round brand marks on the 
rump. It is safe to say that in these instances removal of 
such causes of chronic irritation would eliminate, or at least 
vastly reduce, the occurrence of the cancerous process in 
the situations indicated. In fact, I would go so far as to 
say that, given a dictator’s authority in Australia, and the 
power to enforce effectively that authority, I could diminish 
materially the number of cases of cancer in males by stop- 
ping all smoking, and preventing the occurrence of syphilis! 
There would still, in males, remain a number of cases of 
cancer of the intestinal canal, and in women of the uterus 
and mammary gland. It is almost certain that these also 
owe their origin to some form of chronic irritation. If 
this could be ascertained and removed, how great would be 
the boon to humanity! I am firmly of the opinion that if 
cancer research is to be taken up in Australia the most 
