respiration."  Wiser men than they have been
much further from the truth.
When I practised medicine in the fens, I was
struck by the fact—as doubtless many others
have been—that whenever any of the damp
black earth is turned up, whether in cutting
"turfs" or dykes, or otherwise left exposed to
dry in the sun, it becomes covered with a
distinct white or greyish film. On asking what
this was, I was told that it was the efflorescence
of the salts of the soil. Examination under
the microscope satisfied me that it was not,
but being at the time a young and unpractised
microscopist, I did not guess what it was,
further than that it consisted of a congeries of
simple nucleated cells. In January, 1866, Dr.
Salisbury, an American physician of note,
published, in the American Journal of Science, a
most interesting detail of elaborate experiments
upon this subject. Thereby at last the real
nature of malaria seems to have been ascertained.

The fertile source of desolation and disease
consists of incalculable mvriads of microscopic
cells suspended in the atmosphere over waste,
marshy, and fen districts. They are minute
oblong cells, single or aggregated, and have a
distinct nucleus with a very clear interspace,
apparently empty, between it and the cell wall.
They are of an algoid type, strongly resembling
the palmella, and are consequently among the
lowest organisms known to us. Sometimes
several of these cells, or spores, are contained
in an outer cell wall or delicate investing mem-
brane to form a plant. Of these "ague plants"
is formed that film on the soil to which I have
alluded; and their spores or minute seeds—
germinating cells—rise into the air carrying
pestilence with them. These spores may, I
believe, always be found in the expectoration
of people who have really been seized with
ague.

There are several species of the "ague
plant," which has been called, from the Greek
for earth and the word miasma, Gemiasma.
There are a whiter and a yellowish green
variety, occurring usually on a non-calcareous
soil, and producing agues of but slight intensity.
To the best of my knowledge the white
is the only variety with which we are now
afflicted in England; what other species the
fen men of old time, who had but an aguish
time of it, suffered from when "slimy things
did crawl with legs" on the quaking morass,
when the coot, and bittern, and plaintive
sedge-bird hovered around Whittlesea Mere,
and patches of primeval forest still stood on
the steaming ground, nobody knows, and
nobody ever will know. There are also a
red, a green, and a lead-coloured variety, and
one singular species the "Gemiasma
protuberans," which has larger spores than the
others, and consists of groups of jelly-like pro-
tuberances. These latter kinds habitually occur
on rich calcareous soils, and produce fevers of
a dangerous and congestive character. These
cells with their spores produce visible incrustations
or moulds upon the surface of recently
exposed marsh. The red species causes the
soil to appear as if sprinkled with fine brick-
dust; while of the whiter a familiar instance
occurs in the mildewed appearance of freshly
disturbed fen earth.

The danger from these growths is greatest in
a hot dry season following a wet one. The
wetter the season and the hotter, the better is
it for malaria; the worse for man. In India, it
is during the extreme heat, immediately after
the rains have ceased, that it is most deadly.
At this time the poison is so intense in some
districts that whole tracts of land are deserted.
In Bishop Heber's Narrative of a Journey
through the Upper Provinces of India, speaking
of the vast forests of the Terrai, he says:
"Not the monkey only, but everything that
has the breath of life, instinctively deserts
them from the beginning of April to the end of
October. The tigers go up to the hills, and
the antelopes and wild hogs make incursions
into the plain; and those persons, such as dák
bearers and military officers who are obliged to
traverse the forest in the intervening months,
agree that not so much as a bird can be heard
or seen in all the frightful solitude." He also
speaks of having noticed a dense white mist
brooding in the hollows of the jungle, which the
natives call "essence of owl." This fact I
shall advert to again. An example, showing
that decaying vegetation has nothing whatever
to do with the production of the fungoid marsh
poison, but only the alternation of moisture
and heat acting usually on a peculiar soil, I
take from a paper by Dr. Ferguson, On the
Nature and History of the Marsh Poison, in
the Edinburgh Philosophical Transactions.
"In 1809 several regiments of our army in
Spain took up an encampment in a hilly ravine,
which had lately been a watercourse. Pools of
water still remained here and there among the
rocks, so pure that the soldiers were anxious to
bivouac near them for the sake of using the
water. Several of the men were seized with
violent intermittent fever before they could
move from the bivouac the next morning.

"After the battle of Talavera, the English
army retreated along the course of the Guadiana
river, into the plains of Estremadura. The
country was so dry for want of rain, that the
Guadiana itself, and all the smaller streams had
in fact ceased to be streams, and were no more
than lines of detached pools in the courses that
had formerly been rivers. The troops there
suffered from intermittent fevers of such
malignity that the enemy, and all Europe believed
that the British host was extirpated."

In England, we know comparatively little of
this wide-spread pestilence, which desolates so
considerable a part of the earth's surface.
Formerly, agues were common and dangerous
even here. Both James the First and Cromwell
died of agues caught in London: and it is only
within a few years past that our fen counties
became as healthy as they are now.

Our marsh demon is the veritable "pestilence
that walketh in darkness." It seems