PLEURO-PNEUMONIA IN AUSTRALIA. 
363 
country, and both very badly infected. How it came there none can 
tell. We see cattle migrating from one part of the colony to another, 
and from one colony to another. They are sold, change hands, and, 
though often take long distances, many of them find their way back to 
their old runs. All this has been going on while the disease has been 
raging on the Victorian bank of the Murray. Bullock teams have gone 
and come from one colony to the other, crossing and camping just as 
they liked. Diseased bullocks from some of these teams may have 
been left on runs or strayed away on this side of the Murray. Thus 
the possibility for its introduction here existed in various ways; and 
we know that it was first taken from Boadle’s farm, in Victoria, by 
working bullocks; and we know from the Victorian commissioners’ 
report that working bullocks have strewed the venom of this disease 
across the colony. We know also that working bullocks took it to 
Cambeltown. All history seems, therefore, to point to these migratory 
herds, singling them out as the principal actors in the dissemination of 
the venomous seeds of pleuro-pneumonia epizootiea. 
SPREAD. 
It is a remarkable fact, with respect to pleuro-pneumonia epizootiea, 
that it seems to possess the power of spreading by every known and 
unknown channel. The laws which govern it have never been clearly 
demonstrated, and hence we are startled at its wondrous and rapid 
progress. But we become less and less so the more we know of the 
country, and of the habits of the cattle depasturing in that country. 
Certainly the country is divided into runs, and these are divided in 
many cases by natural boundaries, such as creeks, ranges, and rivers, 
and sometimes only by lines of marked trees. But although these 
lines assist each squatter to know the confines of his runs, yet they do 
not, as a rule, prevent cattle from straying otf their own runs, and they 
mostly roam at freedon where they like, sometimes feeding on their own 
runs, sometimes just over the boundary on their neighbour’s, and some= 
times many miles away from their regular beats. 
It is a law with cattle always to return to the run on which they were 
bred, no matter how great the distance. Some cattle have been known 
to return 600 miles, while 300 is no uncommon distance for them to go 
back. 
Cattle thus returning are subjected to a particular examination by the 
cattle in the various mobs through which they pass on their way back. 
They are strange, and the cattle on these runs surround them on their 
first’appearance, smelling, licking, and butting them; hence, if any 
animal straying in this way possesses any contagious or infectious disease, 
it has a good chance of making rapid progress. 
Coming then to Yarra Yarra and Ten Mile Creek herds, we find part 
of them lately brought to these runs from different districts ; and we 
find many of these cattle afterwards leaving both Messrs. M‘Laurin’s 
and Mr. Bowler’s and making for their old runs, roaming through all 
the stations round, and straying here and there, diseased and not diseased. 
Hence we come to get a clue to the progress of a disease so subtle, 
yet so sure, and we have also a clear explanation of its wondrous 
development among the cattle running on those infected stations specified 
in the Gazette of 24th December, 1861. 
NATURE. 
Pleuro-pneumonia is a disease of a low typhoid nature, showing but 
very slight external symptoms at the period of its incubation—in fact, 
