almost certain that the poison, the spore of the
"ague-plant," only rises into the atmosphere
with the evening dews. Microscopically tested
the day air is free from these organisms. Two
labourers, A and B, shall traverse the same fen
district, both in an equal state of health; but
A shall go through it in the day, and B in the
night when the mist is rising. A returns
home, eats his pork and onion with a relish, and
smokes his post-prandial pipe with much
contentment. But malaria seizes on B, makes
his throat sore, and causes his limbs to ache.
He yawns and shivers, and comes home wretched
and ill.

All fenny districts that are not intensely
malarial, are comparatively harmless in the
day time, and hurtful only when the
innumerable spores of the "ague plants," that
cling throughout the day to the soil, rise at
night, and are suspended in the cold vapours
which hover over the surface of such regions.
But in all malarious districts, to sleep at night
in the open air is almost to ensure an attack of
the disease. It is a fact notorious to seamen
that when off a malarious coast, the sailors can
go on shore during the day with impunity, but
not at night. Here is an instance recorded by
Dr. Lind, an old navy surgeon. In 1766, H.M.S.
Phœnix was returning from the coast of Guinea.
Both officers and men were perfectly healthy
until they touched at the Island of St. Thomas.
Nearly all went on shore, but sixteen of the
crew remained several nights on the island.
Every one of the sixteen was seized by the
disorder, and thirteen of them died. The rest of
the crew, two hundred and eighty in number, who
went on shore at intervals, but who were never
there during the night, entirely escaped
sickness. The reapers in the Campo Morto—
ominously, but aptly, named part of the Maremma
—are allowed to sleep for two hours at noon.
This they do without danger. But it is quite
another thing when the evening dews are falling
on the earth that forms their bed. It is
then that the poisonous mist wraps them in its
deadly winding-sheet. Those who travel through
the Pontine marshes, ought always to do so by
day, if they have a wholesome fear of the
marsh demon before their eyes. "In such
countries," as Sir Thomas Watson racily says,
"'Early to bed' is always a good and wholesome
rule, but the other half of the proverb,
'Early to rise,' becomes a most unsafe precept,"
that is, if early rising implies leaving the house
early. People may (and do) become seasoned to
malaria; become so inured to it that it no longer
produces its specific effects upon them; but they
pay dearly for their seasoning in the degenerated
physique and dull incapable mind that
usually characterises the inhabitant of a
malarious district. In the fens of Cambridgeshire,
immense quantities of alcohol and opium are
taken by the inhabitants to correct the depressing
tendency of the atmosphere.

In different parts of the world these cryptogamic
spores rise in the night mists to different
but definite heights. In Ohio, Dr. Salisbury
says they seldom rise above from thirty-five to
sixty-five feet above the low levels. In England
they do not rise more than from fifteen to
thirty feet. The spores and cells are found
throughout these vapours, but do not extend
above them; and they occur in the greatest
abundance in their upper strata. Three men,
dwellers in aguish places, shall live at different
elevations; one, down in the marsh, on the
low level; one, on the hill side, thirty or forty
feet above; the third, fifty feet higher than
either. Some autumn evening all three issue
out and sit at the doors of their respective huts.
The mist rises from the marsh. In due time
the one living at the lowest level is taken very
ill, the one living next above him is taken very
much worse, while the third, whose house is
highest, suffers nothing, until in an evil moment
he goes down by night to look after his
neighbours, and then he too is laid by the heels.

It has long been known that a certain elevation
gives a sure immunity from intermittents;
and in the neighbourhood of the Pontine
marshes we see the villages perched curiously
on the intervening hills. Near the city of
Lancaster, U.S., resided a certain Mr. and
Mrs. C. Their house was on the edge of a low
terrace and elevated about thirty feet from the
marshy soil around it; there called "the prairie
bottom." About the middle of August, workmen
were excavating in this marshy soil. The
workmen soon began to fall with the ague; at
last nearly all were attacked. On September 1,
Mr. C. was seized with it, and on September 3,
Mrs. C. likewise. The children all remained
quite well. On examining the excavation, the
recently disturbed soil was found covered with
"ague plants." Mr. C. stated that he and
his wife slept in a room on the lower floor,
usually with their windows open; while their
children, seven in number, slept in the second
floor over their own room. He also stated
that early every morning he noticed that
"the fog" from the excavation ground extended
towards the house, rose about two-thirds of the
way up the first story, and freely entered the
window of his room, but he had never noticed
it to rise as high as the room where his children
slept. "The fog" dissipated very early in the
morning before the children were up. He had
lived there forty years and none of his family
had had ague before. This shows how
precisely the height to which the poisonous mist
rises may sometimes be estimated.

Intermittent fever or ague has actually been
intentionally produced in the bodies of men by
causing them to inhale the spores of these
algæ, unknown to themselves; the men
experimented on were exposed to no possible source
of ague, but the one devised specially for them.

Dr. Salisbury tells how he unintentionally
victimised one of his friends. After exhibiting
a large piece of soil covered with the plants of
the gemiasma to his class during lecture, he
placed it under a table in the office of his friend
Dr. House. It was loosely covered with a