76 J. B. CLELAND, 
From the above short resumé of the occurrence of rat 
leprosy in Australia it will be seen that this disease is 
fairly widely distributed, though of relatively rare occur- 
rence. Its incidence amongst the rat population is much 
about the same as the incidence of leprosy amongst the 
human population. Annually in New South Wales several 
cases of leprosy are as a rule notified, and the same pro- 
bably occurs in Queensland, whilst occasional instances are 
found in the Northern Territory and in North-west Aus- 
tralia. For the whole of Australia, during the nine years 
1907 to 1915 inclusive, about 16 new cases were on an av- 
erage reported annually. Indigenous cases of human lep- 
rosy are not known in South Australia, and seem very rare 
in Victoria. On January Ist, 1915, there were 22 human 
lepers in New South Wales, in a population of 1,868,000. 
This is, approximately, 1 leper to 80,000 inhabitants. 
Though in some of the instances of human leprosy in Aus- 
tralia, infection may have occurred outside Australia, in 
quite a number of instances, there is no doubt the patients 
were infected naturally in Australia, as for instance in 
the case of persons who were born in Australia and have 
never been outside it. Whilst in some of these cases as- 
sociation, more or less direct, can be traced to previous lep- 
ers, In other instances no such association can be found. 
It may be roughly stated that whilst about one in 80,000 
of the inhabitants of New South Wales examined at any 
particular time will be found to be leprous, about one in a 
hundred thousand of rats examined in this State may be 
expected to have rat leprosy. Is there any possible connec- 
tion between the two diseases? Are they due to the same 
crganism? Is there any reason to think that if the method 
of spread of rat leprosy could be discovered, the key would 
be found to the solution of the means of spread of human 
leprosy ? 
