_Of the Causes of Fever._
The causes of fever are of two kinds; first, those which immediately
produce the disease, and secondly, those which bring the system into a
condition capable of being affected by the first: the former, are called
the exciting, the latter, the predisposing causes: a third has been
spoken of in relation to this as well as to other diseases, namely, the
proximate. But what is really meant by the proximate cause of disease
(if the term have any meaning) is the condition of the organ, or of the
system, produced by the operation of the exciting cause: this term,
therefore, designates an effect, not in any proper sense, a cause: it
relates to the disease itself, not to that which produces it.
I. OF THE IMMEDIATE, OR EXCITING CAUSE OF FEVER.
The immediate, or the exciting cause of fever is a poison formed by the
corruption or the decomposition of organic matter. Vegetable and animal
matter, during the process of putrefaction, give off a principle, or
give origin to a new compound, which, when applied to the human body,
produces the phenomena constituting fever. What this principle or
compound is, whether it be one of the constituent substances which enter
into the composition of organised matter, or whether the primary
elements of organised matter, as they are disengaged in the process of
putrefaction, enter into some new combination, and thus generate a new
product, we are wholly ignorant. Of the composition of the poison, of
the laws which regulate its formation, and of its properties when
generated, we know nothing beyond its power to strike the human being
with sickness or death. We know that, under certain circumstances,
vegetable and animal substances will putrify: we know that a poison
capable of producing fever will result from this putrefactive process,
and we know nothing more.
Of the conditions which are ascertained to be essential to the
putrefactive process of dead organic substance, whether vegetable or
animal, those of heat and moisture are the most certain, and as far as
we yet know, the most powerful. Accordingly, in every situation in which
circumstances concur to produce great moisture, while the heat is
maintained with some steadiness within a certain range, there the
febrile poison is invariably generated in large quantity, and in great
potency. Wherever generated, we have no means of ascertaining its
existence but by the effects it produces on the human body. Now and then
circumstances arise which illustrate these effects in an exceedingly
striking manner. This is the case when large numbers of men, previously
in a state of sound health, are simultaneously exposed to it. Examples
of such occurrences, as numerous and as complete as can be desired, were
long since recorded, among many others, by one very accurate observer,
who is of the number (no small one) of those who have given valuable
lessons to the world, which have been forgotten, and to which it is a
useful labour to recall the attention of the present age.
“In the beginning of June, 1742,” says Sir John Pringle, in his
Observations on the Diseases of the Army, “the British troops began to
embark for Flanders. There were in all, of foot and cavalry, about
16,000: the winds were favourable, the several passages short, the men
landed in good health, and went into their several garrisons. The
head-quarters were at Ghent. During the Summer and Autumn the weather
was good, the heats moderate, and the country in general healthy. The
British officers continued well, but many of the common men sickened.
Ghent is situated between the high and the low division of Flanders; one
part of the town called St. Peter’s Hill, is much higher than the rest,
and in this, the barracks, having drains and free air, were quite dry;
so that the soldiers who lay there enjoyed perfect health. But those who
were quartered in the lower part of the town (mostly on the
ground-floors of waste houses, unprovided with drains, and of course
damp) were sickly. The battalion of the first regiment of guards was a
remarkable instance of this difference of quarters. Two of the companies
lay on St. Peter’s Hill; the remaining eight in the lower part of the
town, in rooms so very damp, that they could scarce keep their shoes and
belts from moulding. In the month of July, the sick of this battalion
amounted to about 140; of which number only two men belonged to the
companies on the hill, and the rest to those in the lower town.”[31]
It is further stated, that in the end of August, Ostend having
surrendered, the garrison, consisting of five battalions British, was
conducted to Mons, where they continued about three weeks: that these
men had been so healthy that, when they marched out, upon the
capitulation, they left only ten sick; but that the same corps having
been put into damp barracks at Mons, while the town was surrounded with
an inundation, fever immediately appeared, and prevailed to such an
extent, that in this short space of time 250 were seized with the
disease.[32]
Of the campaign in 1748, it is stated that the troops had scarcely been
a month in the cantonments, when the returns of the sick amounted to
2000: that afterwards the number became much greater: that those who
were near the marshes suffered by far the most, both in the number and
the violence of the symptoms; that the Greys, cantoned at Vucht (a
village within a league of Bois-le-duc, surrounded with meadows, either
then under water, or but lately drained) were the most sickly; that for
the first fortnight they had no sick, but, after continuing five weeks
in that situation, they returned about 150; after two months, 260, which
was about half the regiment; and at the end of the campaign, they had in
all but 30 men who had never been ill: that a regiment at Nieuland,
where the meadows had been floated all Winter, and were but just
drained, returned sometimes above half their number: that the Scotch
Fuzileers at Dinther, though lying at a greater distance from the
inundations, yet being quartered in a low and moist village, had above
300 ill at one time, while a regiment of dragoons, cantoned only half a
league south-west of Vucht, were in a good measure exempted from the
distress of their neighbours, such was the advantage even of that
distance from the marshes, of the wind blowing mostly from the dry
grounds, and of a situation upon an open heath, somewhat higher than the
rest.
When the troops were in Zealand, where the poison was in a high degree
of concentration, they had not been a fortnight in the cantonments,
before several of the men belonging to those regiments which were
stationed nearest the inundations, were seized simultaneously with
lassitude and inquietude, a sensation of burning heat, intense thirst,
frequent nausea, sickness and vomiting, aching of the bones, pain in the
back, and violent headache. There were some instances of the head being
so suddenly and violently affected that, without any previous complaint,
the men ran about in a wild manner, and were believed to be mad, till
the solution of the fit by a sweat, and its periodic return, discovered
the true nature of their delirium. Most of the men were first taken ill
upon their return from forage. The regiment being cantoned close upon
the inundations, and many of the quarters being above two leagues from
the place where the magazines were kept, the men were obliged to set out
about four in the morning, in order to get back before the greatest heat
of the day. At this early hour, the meadows and marshes on each side of
the road were covered with a thick fog, of an offensive smell. The party
generally returned before noon; but several of the men, even before they
could get back to their quarters, were already in a violent fever; some,
in this short space of time, were actually delirious; and a few, on
their way home, were so suddenly taken with a phrenzy, as to throw
themselves from their trusses into the water, imagining they were to
swim to their quarters. One man, on reaching home, was suddenly seized
with intense headache, got out of his quarters, and ran about the fields
like one distracted. Three years after this sickness, it was found that
two of the men who were thus suddenly affected with phrenzy, though they
recovered of their fever, had ever since been epileptic, and that all
the rest who had been ill, remained exceedingly liable to returns of an
intermitting fever.
The suddenness with which fever sometimes attacks individuals on board a
ship, or even an entire ship’s crew, on the approach of the vessel to a
shore where this poison is generated in large quantity, and in a high
state of concentration, illustrates its operation, perhaps, in a still
more striking manner. Dr. Maculloch, who has laboured with great ability
and zeal to recal attention to the most important and long-forgotten
subject of malaria, relates an instance of some men on board a ship, who
were seized, while the vessel was five miles from shore with fatal
cholera, the very instant the land-smell first became perceptible.
Several of these men, who were unavoidably employed on deck, died of the
disease in a few hours. The armourer of the ship, who, before he could
protect himself from the noxious blast, was accidentally delayed on deck
a few minutes, to clear an obstruction in the chain cable, was seized
with the malady while in that act, and was dead in a few hours.
Dr. Potter states[33] that he witnessed the rise of a most malignant
yellow fever, in a valley in Pennsylvania, which contained numerous
ponds of fresh water, and which, from the heat and dryness of the
season, emitted a most offensive smell: that the fever prevailed most,
and with the greatest degree of malignity among the people who lived
nearest these ponds; and adds an exceedingly instructive case,
illustrative of the generation and operation of this cause of fever,
recorded by Major Prior, in his account of a fever which attacked the
army of the United States at Galliopolis. The source of the malady was
clearly traced to a large pond near the cantonment. When the disease was
most severe, it assumed the continued form, and was accompanied with
yellowness of the skin: when proper means were taken to destroy the
pond, the fever immediately lost its continued form, and became first
remittent, then intermittent, and ultimately disappeared. “The fever,”
says this intelligent officer, “was, I think, justly charged to a large
pond near the cantonment. An attempt had been made two or three years
before to fill it up, by felling a number of large trees that grew on
and near its margin, and by covering the wood thus fallen with earth.
This intention had not been fulfilled. In August, the weather was
extremely hot, and uncommonly dry: the water had evaporated
considerably, leaving a great quantity of muddy water, with a thick
slimy mixture of putrefying vegetables, which emitted a stench almost
intolerable. The inhabitants of the village, principally French, and
very poor, as well as filthy in their mode of living, began to suffer
first, and died so rapidly, that a general consternation seized the
whole settlement. The garrison continued healthy for some days, and we
began to console ourselves with the hope that we should escape
altogether: we were, however, soon undeceived, and the reason of our
exemption heretofore was soon discovered. The wind had blown the air
arising from the pond from the camp; but, as soon as it shifted to the
reverse point, the soldiers began to sicken: in five days, half the
garrison was on the sick list, and in ten, half of them were dead. They
were generally seized with a chill, followed by headache, pains in the
back and limbs, red eyes, constant sickness at stomach, or vomiting, and
generally, just before death, with a vomiting of matter like
coffee-grounds. They were often yellow before, but almost always after
death. The sick died generally on the seventh, ninth, and eleventh days,
though sometimes on the fifth, and on the third. As some decisive
measures became necessary to save the remainder of the troops, I first
thought of changing my quarters, but as the station was in every respect
more eligible than any other, and had been made so by much labour and
expense, I determined to try the experiment of changing the condition of
the pond, from which the disease was believed to have arisen. A ditch
was accordingly cut; what little water remained was conveyed off, and
the whole surface covered with fresh earth. The effects of this scheme
were soon obvious. Not a man was seized with the worst form of the fever
after the work was finished, and the sick were not a little benefitted,
for they generally recovered, though slowly, because the fever became a
common remittent, or gradually assumed the intermitting form. A few
cases of remitting and intermitting fever occurred occasionally, till
frost put an end to it in every form. As soon as the contents of the
pond were changed, by cutting the ditch, the cause, whatever it was,
seems to have been rendered incapable of communicating the disease in
its worst form.”
Dr. Potter further states that, on one occasion, he saw a lady, who had
been confined three days only, and whom he found in the agonies of
death, with the skin of a deep orange colour, the eyes red and
prominent, the pulse intermittent, and ejecting copiously from the
stomach every eight or ten minutes, the secretion now known by the name
of the black vomit; that she expired in a convulsion, while he sat at
her side; that petechiæ appeared immediately after death, and that
putrefaction succeeded so rapidly, that it was necessary to order
immediate interment: that, shortly afterwards, he was called to a
gentleman who had been ill five days, and who, having expired in an hour
or two after his visit, was removed into the coffin with the utmost
difficulty, the flesh literally dropping from the bones: that, in one
family residing in a house which stood on a level piece of ground,
apparently beyond the reach of noxious exhalation, there being no
stagnant water, as was supposed, within a mile of it, he found the
mother labouring under a bilious remitting fever, which had continued
eleven days; the daughter, seventeen years of age, suffering from a
similar fever; two sons, the one between eight and nine, and the other
six, ill with dysentery; and the father, on the brink of the grave, from
a most malignant fever. There being no apparent cause for the condition
of this afflicted family, the immediate neighbourhood of the house being
free from the ordinary sources of malaria, and the adjacent country
being not unhealthy, the condition of the house itself was minutely
investigated. The cause of the evil was manifest. It appeared that the
present family had resided in the house only about five weeks; that
immediately preceding their occupation of it, a man had died suddenly in
it; that he himself (Dr. Potter) was seized with nausea and general
lassitude, immediately on leaving the house after his first visit; and
that a fever, as he supposes, was arrested by a strong dose of
tartarized antimony, which operated violently by vomiting and purging.
On examining the premises, it was found that the cellar contained water
about two feet deep, which had remained there from the first week in
June, the country having been then inundated by torrents of rain. The
cellar being useless, the door had been closed, and the only vent for
the pestiferous gases was through the floor, which was open in several
places. The family being immediately removed, all the sick became
convalescent from the time they ceased to breathe the air of the place.
The owner of the house hired two men to empty the cellar. These men
having ripped up the floor, and placed a pump in the deepest part of the
water, evacuated the cellar to the dregs in one day. On the second day
after the execution of this task, one of these men was seized with a
chilliness, succeeded by an ardent fever, which terminated with the
usual symptoms of yellow fever; namely, hæmorrhages, yellow skin and
petechiæ, and proved fatal on the third day from the attack: the day
following the seizure of the first, the second man was attacked with
similar symptoms, and died on the seventh day of the disease, with the
black vomit, in addition to the ordinary symptoms of the yellow fever.
These examples may suffice to illustrate the operation of that febrile
poison which arises chiefly from the decomposition of vegetable matter.
The poison derived from the putrefaction of animal matter is still more
pernicious: its effects are more powerful in degree, and worse in
character; it operates more intensely on the nervous system, and less on
the vascular; and the fevers it produces are invariably of the typhoid
type, and of the continued form.
Without doubt, a febrile poison, purely of animal origin, in a high
degree of concentration, would kill instantaneously; and when not
intense enough to strike with instantaneous death, it would produce a
continued fever with the typhoid characters, in the greatest possible
degree of completeness and perfection. And this appears to afford the
true solution of the origin of the plague. The more closely the
localities are examined of every situation in which the plague prevails,
the more abundant the sources of putrefying animal matter will appear,
and the more manifest it will become, not only that such matter must be
present, but that it must abound. And this also is one of the truths
which was known to the observers of former times, but which has been
forgotten. Were it not that the professional reading of an age, is
bounded by as strict a line as that which divides century from century;
were it not that no one reads back beyond the authority which happens to
give to the day its prevailing doctrines; were it not that the great
repository of facts treasured up in the volumes of the close observers,
though sometimes the bad reasoners of former days, thus becomes
neglected for the dogmas of some modern writer, who reasons as ill, and
who observes less, the notion that vegetable malaria produces only
intermittent fever, never could have become so prevalent as it is at
present, nor could the influence of animal malaria ever have been so
entirely overlooked. But it chanced that Cullen, in his definition of
intermittent fever, assigned the miasma of marshes as the origin of the
disease, while he makes no mention of animal malaria in his definition
of any of the forms of fever; and as this author superseded all former
authorities, by becoming the great authority of the age, few of his
successors are acquainted in the slightest degree with the writings
anterior to his period: whence it has happened that the numerous and
invaluable facts observed and recorded by his predecessors, relative to
the cause of fever, have been disregarded until they have become wholly
unknown. To cite the antient and the more modern authorities who have
observed and recorded the influence of animal malaria in the product of
plague, would be to enumerate every distinguished writer, from Pliny and
Diodorus Sicculus, down to Galen, from Galen to Mead, and from Mead to
Pringle.
In assigning the reason why Grand Cairo, in Egypt, is the birth-place
and the cradle of the plague, Mead states that this city is crowded with
vast numbers of inhabitants, who live not only poorly, but nastily; that
the streets are narrow and close; that the city itself is situated in a
sandy plain, at the foot of a mountain, which keeps off the winds that
might refresh the air; that consequently the heat is rendered extremely
stifling; that a great canal passes through the midst of the city, which
at the overflowing of the Nile is filled with water; that on the
decrease of the river, this canal is gradually dried up, and the people
throw into it all manner of filth, carrion, offal, and so on; that the
stench which arises from this, and the mud together, is intolerably
offensive; and that, from this source, the plague constantly springing
up every year, preys upon the inhabitants, and is stopped only by the
return of the Nile, the overflowing of which washes away this load of
filth: that in Ethiopia the swarms of locusts are so prodigious, that
they sometimes cause a famine, by devouring the fruits of the earth, and
when they die, create a pestilence, by the putrefaction of their bodies;
that this putrefaction is greatly increased by the dampness of the
climate which, during the sultry heats of July and August, is often
excessive; that the effluvia which arise from this immense quantity of
putrefying animal substance, combined with so much heat and moisture,
continually generate the plague in its intensest form; and that the
Egyptians of old were so sensible how much the putrefaction of dead
animals contributed towards breeding the plague, that they worshipped
the bird Ibis, from the services it did in devouring great numbers of
serpents, which they observed injured by their stench when dead, as much
as by their bite when alive.
Nothing can be more striking than the cases recorded by Pringle, and
which daily occurred to him of the production of fever, exquisitely
typhoid, (according to the language of that day, jail and hospital
fever) and of the sudden transition of intermittent and remittent into
the continued and typhoid type, from the presence of a poison clearly
and certainly of animal origin. Whenever wounded soldiers, with
malignant sores, or mortified limbs, were crowded together, or whenever
only a few of such diseased persons were placed in a room with the sick
from other diseases, with those labouring under intermittent and
remittent, for example, a severe and mortal typhus immediately arose;
nay, whenever men, previously in a state of sound health, were too much
crowded together for any considerable time, typhus (jail or hospital
fever) was sure to be produced. The instances of such occurrences that
are detailed, are too numerous to be cited, but they are so clearly
stated, and so striking, that they well deserve to be consulted by
whoever is desirous of clearly tracing the operation of this great cause
of fever.
But by far the most potent febrile poison, derived from an animal
origin, is that which is formed by exhalations given off from the living
bodies of those who are affected with fever, especially when such
exhalations are pent up in a close and confined apartment. The room of a
fever-patient, in a small and heated apartment in London, with no
perflation of fresh air, is perfectly analogous to a stagnant pool in
Ethiopia, full of the bodies of dead locusts. The poison generated in
both cases is the same; the difference is merely in the degree of its
potency. Nature, with her burning sun, her stilled and pent-up wind, her
stagnant and teeming marsh, manufactures plague on a large and fearful
scale: poverty in her hut, covered with her rags, surrounded with her
filth, striving with all her might, to keep out the pure air, and to
increase the heat, imitates nature but too successfully; the process and
the product are the same, the only difference is in the magnitude of the
result. Penury and ignorance can thus at any time, and in any place,
create a mortal plague. And of this no one has ever doubted. Of the
power of the living body, even when in sound health, much more when in
disease, and above all, when that disease is fever, to produce a poison
capable of generating fever, no one disputes, and the fact has never
been called in question. Thus far the agreement among all medical men,
of all sects, and of all ages, is perfect.
But it happens that there is another form of animal matter capable of
producing fever: namely, a matter secreted by the living body,
constituting not only a poison, but a peculiar and specific poison. This
specific poison produces not merely fever, but fever with a specific
train of symptoms. In the acknowledgment of this fact, also, the
agreement among all medical men is equally perfect.
But some contend that the poison generated in the first case, and that
generated in the second, may both be properly called contagions: others
maintain that the application of the same term to two cases so
specifically different, destroys a distinction which it is useful to
preserve, and that it would be more correct, as well as more conducive
to clearness of conception, to call the poison generated in the first
case an infection, and to restrict the term contagion, to designate the
poison generated in the latter. Vast and immeasurable as the difference
appears to be between the contagionists and the anti-contagionists, if
regard be had merely to their language, yet if attention be paid only to
their ideas, to this, and to this only, narrow as the compass is, the
whole controversy is reduced. It resolves itself wholly into the
question, whether one word shall be used to express two cases which
differ from each other in some important circumstances, or whether it
may not be more convenient to employ two terms, and strictly to
appropriate each to designate its own specific class. It must be
manifest that, since both sects are perfectly agreed about the facts,
the dispute can be only verbal. If the one would consent to restrict
their use of the term contagious, for which there is the best authority
and ancient custom, to those diseases which arise from a specific
contagion, and would call those which arise from every other poison
infectious, there would be an end to this apparently interminable, and
in many respects mischievous, controversy.
Is the febrile poison, whether of vegetable or animal origin, or whether
composed of both, capable of adhering to clothes, apparel, and other
substances, in such a manner as truly to infect them, so that when
applied to the bodies of the healthy, at any distance of place, and at
some distance of time, the specific effects of the poison are produced?
That such substances may be so imbued with the poison of the small-pox,
all admit: that the evidence should not be as complete relative to the
power, or the inability of such substances to convey and communicate the
poison of ordinary continued fever, is alike disgraceful to the state of
our science, and injurious to the cause of humanity. There is no reason
why the question should not be settled with absolute certainty; there is
no manner of difficulty in determining it. Experiments the most direct,
complete, and decisive, might be performed, which, if observed, during
their progress, by competent witnesses, and duly authenticated, might
ascertain the point with sufficient clearness and certainty, to satisfy
not only the present age, but future generations. Once, for all, the
full trial might be made, and if the trial were really full, it need
never be repeated. A series of experiments completely decisive of the
question, as far as regards the fever of our own country, which might be
easily extended to the plague, were some time ago drawn out, and
exertions were made to carry them into effect; but in the prevailing
state of public opinion and feeling, it was found absolutely impossible
to institute them on a scale at all adequate to render them decisive,
without the aid of Government. There seems to be no possible mode of
performing them effectually, unless Government will co-operate, by
granting a free pardon to such convicts, as will voluntarily allow
themselves to be made the subjects of them. The risk to them would be
slight, the evil to the community none; while the danger, the suffering,
the disease, the mortality that would be prevented, to say nothing of
the expense that would be spared by the decision of the question, would
be incalculable. It is earnestly to be hoped that those who have it in
their power to afford the means of putting this question at rest, will
not allow it to remain in its present unsettled state. Science,
commerce, humanity, alike demand that the truth should be ascertained.
This subject, it is my intention to take up, and to discuss fully in a
future publication, in which will also be investigated some inquiries,
which it has been found impossible to include in the present volume;
such as whether the vegetable and animal poison we have been
considering, be the only true exciting cause of fever; by what means its
general diffusion is effected; on what conditions its propagation
depends; by what measures its extension may be checked, and its power
diminished or destroyed; what circumstances in the modes of life, in the
habits of society, in the structure of houses, in the condition of the
public streets and the common sewers, in the state of the soil over
large districts of the country, as influenced by the mode of
agriculture, drainage, and so on, favour or check the origin and
propagation of this great curse of civilized, no less than of
uncivilized man. It is obvious that these inquiries will include the
investigation of several exceedingly curious and important statistical
questions; and the object of these researches will be accomplished
should they lead to the establishment of any useful principles of
extensive application.[34]
II. OF THE REMOTE OR PREDISPOSING CAUSES OF FEVER.
The remote or the predisposing causes of fever have been stated to be
those circumstances which bring the body into a condition capable of
being affected by the immediate or the exciting cause. Whatever
diminishes the vigorous action of the organs, impairs their functions,
and so weakens the general strength of the system, is capable of
becoming a predisposing cause of fever; and every predisposing cause
acts in one or other of these modes, and becomes a predisposing cause
only and in proportion as it lessens the energy of the system, or
disturbs the balance of its actions, which in fact is to render some
portion of it weak. During a state of vigorous health the body is
endowed with the power of resisting the influence of noxious agents,
which in a less perfect state of health are capable of producing intense
and fatal disease; and the action of all predisposing causes is to
lessen this resisting power, or to weaken the energies of life.
Of all predisposing causes, the most powerful is the continued presence
and the slow operation of the immediate or the exciting cause. It is a
matter of constant observation, that the febrile poison may be present
in sufficient intensity to affect the health, without being sufficiently
potent to produce fever. In this case the energy of the action of the
organs is diminished, their functions are languidly performed, the
entire system is weakened, and this increases, until at length the power
of resistance is less than the power of the poison. Whenever this
happens, fever is induced; not that the power of the poison may be at
all increased; but the condition of the system is changed, in
consequence of which, it is capable of offering to the noxious agent
that assails it less resistance.
We have seen that the vegetable or animal poison may exist in sufficient
intensity to produce fever on the slightest exposure to it, without the
operation of any predisposing cause, in a body in the state of the
soundest health, and endowed with the greatest degree of strength.
Examples of this kind are but too frequent in tropical climates. In
countries where the temperature never rises so high, and seldom
continues so long, it is rare that fever is produced immediately, on
exposure to the exciting cause. Concentrated and potent as that poison
is in many parts of Flanders, yet Sir John Pringle states that, in
removing to an unhealthy situation, the men rarely became ill at once;
that they generally continued in tolerable health for some days; and
that recruits recently arrived in the country, resisted the noxious
agent longer than the men who had been long there. Dr. Potter gives a
remarkable example of the same fact, with regard to the yellow fever,
which fell under his own observation, and states other facts, strikingly
illustrative of the influence and operation of the predisposing causes.
Strangers, from certain countries, he informs us, are insusceptible of
yellow fever in America. In the most malignant and protracted epidemics
which afflict that country, these strangers uniformly escape: emigrants
from the West Indies, and other warm latitudes, for example, invariably
resist the cause which produces these maladies in the native
inhabitants. But the curious fact is, that such persons are unable
permanently to resist the operation of the exciting cause; for, after a
residence in America of some years, their constitution is so completely
assimilated by the influence of the climate to that of the American,
that they become equally sensible to its febrile miasma, and are as
exquisitely impressed by them, as the American citizens themselves. The
illustration is equally striking and instructive, if the position be
reversed. The natives of northern climates are extremely susceptible to
the influence of these miasma; that susceptibility is in exact
proportion to the latitude of their country: those from the north of
Europe scarcely ever escape an attack; the natives of Great Britain are
nearly as susceptible to the influence of the poison, while persons even
from the more northern countries of the United States are more liable to
the disease than the citizens of the southern and middle states.
Dr. Potter performed some experiments, to show that the continual
presence of the exciting cause not only operates upon the general
system, but actually produces a morbid change in the blood, before it
induces fever. During the prevalence of an epidemic, it was observed
that, in all the cases in which the patients were bled, the general
appearance of the blood was precisely the same; that the coagulum was
either of a yellow, or of a deep orange colour, and that a portion of
the red particles was invariably precipitated. It occurred to Dr. Potter
that, if the cause of the disease were contained in the common
atmosphere, the blood of those who had inhaled it a certain time would
exhibit similar phenomena; and that, should this be the case, it would
prove that the cause, before actually producing the disease, brought
about a state of the system, which predisposed it to be affected by the
poison. To ascertain the appearances of the blood in persons who were
exposed to the febrile poison, but who still remained apparently in
perfect health, he drew a quantity of blood from five persons, who had
lived during the whole epidemic season in the most infected parts of the
city. To external appearance and inward feeling, each of these persons
was in sound health. Their blood could in no respect be distinguished
from the blood of those who laboured under the most intense forms of the
prevailing fever. As it was necessary to the conclusiveness of the
experiment that their blood should be compared with the blood of those
who lived in an atmosphere unquestionably pure, Dr. Potter selected an
equal number of persons who dwelt on the hills in Baltimore country, and
drew from each of them ten ounces of blood. The contrast was most
manifest. The serum was neither of a yellow, nor of an orange colour;
there was no red precipitate; the appearances were such as are found in
the blood of persons in perfect health.
A young gentleman having returned to the city from the western part of
Pennsylvania, on the 10th of September, in a state of sound health, Dr.
Potter drew a few ounces of blood from a vein, on the day of his
arrival; it exhibited no deviation from that of a healthy person. He
remained in the family until the 26th of the month, that is sixteen
days. On the 16th day the bleeding was repeated. The serum had assumed a
deep yellow hue, and a copious precipitation of red globules had
likewise fallen to the bottom of the vessel.
In these experiments, the blood in six persons indicated the operation
of the morbid cause, while each remained in a state of apparent health.
Of these six persons, four were actually seized with yellow fever during
the prevalence of the epidemic; and the other two, though they escaped
any formal attack, did not escape indisposition. They were affected with
headache, nausea, and other indications of disease, like hundreds
besides, who were never absolutely confined to the house, and who never
took any medicine, but who still experienced in nausea, giddiness,
headache, pain in the extremities, and so on, abundant intimations of
the presence of the poison.
These examples may suffice to show how the exciting, may itself become a
most powerful predisposing cause. The predisposition to subsequent
attacks, after the system has once suffered from the disease, is very
remarkable; that predisposition remains for a considerable period after
convalescence and apparent recovery. Of this, striking examples
continually occur both with regard to intermittent, and to continued
fever. In fact, the disposition to relapse, remains until the
constitution has recovered its previous strength and vigour, however
distant that period may be. The influence of cold, moisture, fatigue,
intemperance, constipation, anxiety, fear, and all the depressing
passions, are likewise extremely powerful predisposing causes. They
enable a less dose of the poison to produce fever, and they increase the
intensity of the fever when it is established. They all act by weakening
the resisting power inherent in the constitution, that is, by enfeebling
the powers of life.