the insect bites mainly just following daybreak, when the victim is
profoundly unconscious in sleep, its presence often remains undetected,
and as a consequence we occasionally hear from those who do not take the
trouble to inform themselves that malaria exists in this or that locality
where mosquitoes do not occur.

The yellow-fever mosquito bites for the most part during the day, but
will do so at any time when there is light. In districts where this
disease occurs it is quite as important to prevent its entrance as that
of the malarial mosquito. Not only does screening prevent malaria and
yellow fever, but it keeps out flies and other insects that
unquestionably bring with them the germs of other diseases.

There now remains no doubt that several affections, notably typhoid fever
and dysentery, are frequently communicated by means of the common
house-fly, which spends its time alternately on the fecal material around
privies or in other filth, and in our kitchens and dining-rooms; it is
one of the most astounding evidences of the power of habit, in the face
of common sense and ordinary decency, that we have not long ago taken
active steps to rid ourselves of its disgusting presence. Fortunately in
screens we have a perfect barrier to the entrance of flies, and no house
can be considered complete without being thoroughly equipped with these
all-necessary appliances.

It is scarcely possible to overestimate the economy that results from the
use of screens; among the various means employed for conserving the
public health they take first rank, and undoubtedly insure those who live
in houses to which they have been added an immunity against the costly
effects of disease that could scarcely be computed. A house would be more
habitable without chairs, beds, or tables than screens, since in the
absence of the former we may be healthy, though somewhat uncomfortable,
but without the latter serious disorders are pretty certain, sooner or
later, to make their appearance.

It is of considerable importance to use a screen the mesh of which is
sufficiently fine. Where mosquitoes exist, the screen should be of such
fineness that at least sixteen, or better eighteen meshes be in each inch
of the gauze. Where it is absolutely certain that mosquitoes are not to
be feared, the spaces may be somewhat larger--but always of such size as
will prevent the entrance of the smallest fly.

_Air-space Required._--It is of much importance fro