PRESIDENTIAL ADDRESS. 9] 
What are the causes at work in stimulating this latent 
gvametoid capacity of the cells? I believe that many forms 
of chronic irritation and conditions leading to stress and 
strain in the normal functioning of somatic cells may be 
responsible. The cells multiply unduly rapidly, and do so 
exposed to noxious influences. They have probably nor- 
mally a limit to the number of somatic divisions they can 
undergo. This limit is reduced under these circumstances. 
They therefore become old before their time, whilst the 
previously dominant somatic factors are handicapped. 
Extinction or rejuvenation of the group of cells concerned 
are the only alternatives. Sometimes the former occurs, and 
we get necrosis of tissues. Sometimes the latter, and a 
eancer results. 
If this view is correct, then one of the main objects of 
cancer research should be to ascertain the factors, often 
obscure, that set up such chronic irritations. We know 
them fairly well in the cases of the lip and tongue. If we 
could discover them and remove them early in the cases of 
the mammary gland, the uterus and stomach, numbers of 
lives might be saved. If cancer research is to be conducted 
in Australia, I would most strongly advocate attention in 
this direction as being by far the most promising field for 
productive results. This aspect is referred to again in the 
next section. 
CANCEROUS GROWTHS IN Rats AND MICE. 
Rats and mice, like a number of other vertebrates, are 
subject to malignant growths, both carcinomata and sarco- 
mata. The recognition of these tumours in any species, 
whether the various races of man or a lower animal, is 
probably dependent in great part on the number of indi- 
viduals of the species (or race) available for examination, 
the average span of life of these individuals as compared 
with the natural length of life, and the degree to 
