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cent is imported from purely country districts of those under 
20 years of age ; and of 26 per cent over 20 years. This 
constitution of replenishment of towns, associated with what 
is subsequently shown, large mortality at early ages , leads to 
the view that considerable drafts from the country from 15 
years upwards are made by towns, and which latter are 
responsible for their health. 
With the exception of infantile diseases, those of 15 to 55 
years ol age are the most fatal, and towns present a large 
field for the operation of disease at that age. 
The diseases of infancy and childhood are in a great degree 
infectious. Hence density of population would be considered 
a great element of mischief at those periods ; but smallpox, 
scarlet fever, and some others, more infectious than others, 
present a less increase of mortality than measles over that of 
the country. The same law will apply to fever, influenza, 
and others at a later age — density and infection do not obey 
the same law of proportionate increase: neither will Dr. 
Farr’s formula, for mortality increasing according to a certain 
root of the density, apply to provincial towns. 
Imprudent and early marriage, and inebriety have a certain 
value in the production of town mortality, but only to a' 
slight extent, especially as to the former ; the latter evil is 
not productive of so great an increase in the direct disease 
consequent upon it as materially to elevate town mortality 
over that of the country. 
Atmospheric causes, those from malarious mischief, in this 
Paper are not entered upon to any extent : they have a 
variable value, which is balanced to a great extent by the 
higher rate of income and consequent improvement of 
sustenance. 
The centralising system of this century is in itself not, 
therefore, it would appear, a great bane to the country ; and 
yet towns kill considerably greater numbers of people than 
the country. There is an element of destruction which 
