milar results from his investigations in other parts of the
kingdom, and says:--

"It may, therefore, be safely asserted as regards England generally,
that:--

"The diseases which have been made the subject of the present inquiry,
have been steadily decreasing, both in frequency and severity, for several
years, _and this decrease is attributed, in nearly every case, mainly to
one cause,--improved land drainage;_" again:

"The change of local circumstances, unanimously declared to be the most
immediate in influencing the prevalence of malarious diseases, is land
drainage;" and again:

"Except in a few cases in which medical men believed that these affections
began to decline previously to the improved drainage of the places
mentioned, the decrease in all of the districts where extensive drainage
has been carried out, was stated to have commenced about the same time,
and was unhesitatingly attributed to that cause."

A select Committee of the House of Commons, appointed to investigate the
condition and sanitary influence of the Thames marshes, reported their
minutes of evidence, and their deductions therefrom, in 1854, The
following is extracted from their report:

"It appears from the evidence of highly intelligent and eminent gentlemen
of the medical profession, residing in the neighborhood of the marshes on
both sides of the Thames below London Bridge, that the diseases prevalent
in these districts are highly indicative of malarious influences,
fever-and-ague being very prevalent; and that the sickness and mortality
are greatest in those localities which adjoin imperfectly drained lands,
and far exceed the usual average; and that ague and allied disorders
frequently extend to the high grounds in the vicinity. In those districts
where a partial drainage has been effected, a corresponding improvement in
the health of the inhabitants is perceptible."

In the evidence given before the committee, Dr. P. Bossey testified that
the malaria from salt marshes varied in intensity, being most active in
the morning and in the Summer season. The marshes are sometimes covered by
a little fog, usually not more than three feet thick, which is of a very
offensive odor, and detrimental to health. Away from the marshes, there is
a greater tendency to disease on the side toward which the prevailing
winds blow.

Dr. James Stewart testified that the effect of malaria was greatest when
very hot weather succeeds heavy rain or floods.