246 
Village Sanitary Economy. 
miasmatic exhalations may arise and find their way back as 
malaria to the village. Too little is known of the combined effect 
of evaporation from a wet surface when associated with exhala- 
tions from organic matter; but judging from the experiences of 
foreign countries, where malaria abounds, it would appear to be 
an undoubted fact that wherever organic matter is evolved at tlie 
same time and from the same surface that water is evaporated, 
malaria of a deadly character becomes localised. The Reports 
of the Registrar-General distinctly show that the health of towns 
in this country has been immediately improved wherever the 
effect of the sewers has been to lower the water in the subsoil, 
and evaporation has been reduced. Hence it follows that to avoid 
all chance of malaria arising from land to which sewage is applied, 
the soil should be either of a free and open description, allowing 
the liquid sewage to descend for a considerable depth before it 
reaches the level of the springs, or where such a description of 
soil cannot be obtained, and a soil of tenacious character must be 
resorted to, then that under-drainage, laid out with regard to the 
system of surface irrigation, should be adopted to enable the 
sewage to pass through sufficient earth to become purified before 
it reaches the outlets. Up to this time the opinion has prevailed 
that the passage of sewage over a surface of growing vegetation 
is sufficient to purify it. This opinion, however, is entertained 
only by a few recognised authorities. After feeding vegetation, 
it is desirable that the effluent sewage should pass throuyli a 
considerable quantity of soil before it is discharged into the rivers ; 
the drains, therefore, where clay lands are used, should be as deep 
as possible, in order to increase the downward filtration, and should 
be as distant from each other as is consistent with effective perco- 
lation. By thus increasing, horizontally as well as vertically, the 
amount of soil through which the sewage will travel, it will be- 
come oxygenised in the same way as is the case with sewage passing 
several miles down a river. Under any circumstances, the condi- 
tion of the effluent water when it leaves the subsoil will approach 
much nearer purity than can be the case where the sewage passes 
over the surface only, or where the drains are laid out without 
strict regard to the system of irrigation adopted on the surface. 
Instances exist where the under-drains have passed directly under 
the surface carriers, and having received the sewage direct from 
them, have discharged it into the rivers in a state very little 
different from what it was when it left the sewers; but this is 
wholly caused by injudicious construction of works, though the 
circumstance has been quoted, without explanation, as a reason 
for not draining sewage irrigated lands. 
It is stated by the Rivers Commissioners, in their first Report, 
that the extent of land in proportion to population to which 
