ECONOMIC EFFECTS OF SANITARY WORKS. 123 
two principal domestic requirements of water supply and 
sewerage, for though there are other services such as col- 
lection of garbage and the cleansing of the public streets, 
which improve the sanitary condition of towns, there can 
be no question that a copious supply of water at a high 
pressure, and a system of sewers that will remove all 
impurities from dwellings are of the greatest importance 
in conserving the public health, and experience teaches us 
that they are the primary factors in reducing the death 
rate; moreover, the fact has been proved by statistics in 
scores of places, where the effects of water supply and 
sewerage works on the public health have been under close 
scrutiny for many years. For instance, in London the 
average death rate of 24°8 per thousand for the decennial 
period ending 1850 has been reduced to 19°5 per thousand 
for the decennial period ending 1890, in Glasgow the death 
rate has been reduced from 56 in 1847 to 25 in 1893, in 
Sydney the average death rate of 21°02 for 15 years ending 
1885 has been reduced to 15°38 for the 15 years ending 1900, 
and similar results can be seen from the record of other 
places given in the appendix (A); the periods embraced by 
these statistics are those during which water supply and 
sewerage works have been actively progressing. With 
regard to the relative importance of each of these two 
services, that of water supply has always been in the 
greatest demand and the most popular with the general 
public, the question of sewerage being deferred to a later 
period or until such time as the increased death rate from 
typhoid and other zymotic diseases has been forced upon 
the attention of the public, but sanitary engineers and 
scientists have always considered both services of equal 
importance to the public health ; owing to the lack of data 
it is impossible to differentiate the benefits arising from 
each system, but the general experience has been that for 
a short time after the installation of a water supply the: 
