interest, and has been the subject of much controversy. The great
rapidity of the spread of epidemics, the vast area they overrun, the
fact that they do not follow the lines of human intercourse, the
suddenness with which great numbers of the inhabitants of an invaded
district or city are seized, the fact that the most complete seclusion
from intercourse with affected persons, or even the shutting up of
houses, affords in most instances no protection whatever,--all go to
show that the disease spreads, in the main, independently of direct
contact. This opinion has been almost universally entertained. There
is evidence, however, to show that the disease is to some extent
contagious; and so convincing have the facts bearing upon this point
appeared to some that they have believed it to be propagated entirely
by human intercourse. Haygarth[16] declares, as the result of his
observations during the epidemics of 1775 and 1782, that the influenza
spreads "by the contagion of patients in the distemper;" and
Falconer,[17] writing of the epidemic of 1803, says, "I have no doubt
that it is contagious in the strictest sense of the word." Watson[18]
regards the instances in which the complaint has first broken out in
those particular houses of a town at which travellers have arrived
from infected places as too numerous to be attributed to mere chance.
Very often those dwelling near the invalids are attacked next in the
order of time, and when the disease affects a household all do not
usually manifest the symptoms at the same time, but one member after
another is stricken down with it.
[Footnote 16: John Haygarth, M.D., F.R.S., _On the Manner in which the
Influenza of 1775 and 1782 spread by Contagion in Chester and its
Neighborhood._]
[Footnote 17: William Falconer, M.D., F.R.S., _An Account of the
Epidemic Catarrhal Fever, commonly called the Influenza, as it
appeared at Bath in the Winter and Spring of the Year 1803_, Bath,
1803.]
[Footnote 18: _Principles and Practice of Medicine_.]
In a few rare cases the isolation or seclusion of a community has
appeared to give protection, as in cloisters, prisons, garrisons, and
the like; at all events, there are instances on record where
segregated communities of this kind have escaped attack.
The following observation, conducted under unusual circumstances,
establishes the fact that influenza may be brought from an infected
city in such a way as to give rise to a localized outbreak in a remote
community. Drs. Guitéras and White[19] narrate that, influenza
prevailing in Europe, and particularly in Paris and London, an
American gentleman in bad health contracted the disease in London,
improved, suffered a relapse {863} shortly afterward in Paris, and
died there at the end of December, 1879. His body was embalmed and
sent home. Following the exposure of the remains of this person to the
view of his family in Philadelphia there was an outbreak of influenza
with characteristic symptoms, which affected, in the first place,
members of that family; afterward, friends living in close intercourse
with them; next, the medical attendant of some of them; and finally,
the housekeeper and a patient or two of one of the physicians who
wrote the paper, the whole number affected in Philadelphia being
eighteen at the time of the publication of the account. Subsequently
two or three other cases were developed, but the disease did not
extend beyond the immediate circle of those in direct communication
with the invalids.
[Footnote 19: John Guitéras, M.D., and J. W. White, M.D., "A
Contribution to the History of Influenza, being a Study of a Series of
Cases," _Philadelphia Medical Times_, April 10, 1880.]
It was at one time thought that influenza developed at once, without a
period of incubation, persons in perfect health being struck down with
it as by lightning-stroke. It is, however, now known that a period of
incubation, varying from a few hours to several days, and usually
without subjective symptoms, exists. Many instances are recorded in
which persons coming into an infected city have remained well for one,
two, or three days, but have eventually shared the sufferings of those
into whose midst they have come. There are cases also in which the
period of incubation could not have been less than two or three weeks.
There is no sufficient evidence of a causal relation between influenza
and any other epidemic disease. The statement that other prevalent
diseases abate in frequency and intensity upon its outbreak is not
sustained by well-observed facts. Graves[20] holds that those
suffering with acute diseases are less liable during the febrile
stage, but that they are attacked as convalescence sets in.
[Footnote 20: _Clinical Medicine_.]
The facts in reference to the spread of epidemics of influenza and the
course of the disease in infected localities are comprehensible upon
no other theory than that of a specific infecting principle as its
exciting cause. What this principle may be is not yet known; where it
originates is equally unknown; and our knowledge of the influences
that from time to time call it into activity and send it forth in
definite directions over the earth is no less negative.
So general a disease can only be disseminated by the most general
medium, the atmosphere, and its exciting cause must be capable of
reproducing itself in that medium, otherwise it would be lost by
dispersion in traversing distances measured by the boundaries of
continents and oceans. The rapid diffusion of influenza, sweeping over
continents in a few weeks at one time, its slow migration, creeping
about a city and its environs for months, at another, are to be most
easily explained upon the theory of a living miasm capable of being
transmitted by the air, and possessing at the same time an independent
existence. Such an entity would find certain localities more favorable
to its growth, reproduction, and prolonged existence than others. From
this point of view influenza is a miasmatic disease. The infecting
principle of this disease is also, to a slight extent, capable of
being reproduced in or about the human body and transmitted by
personal intercourse, as well as conveyed from place to place by the
persons or clothing of those affected or those travelling from
localities in which the disease prevails. We are thus led to the
conclusion that it is also contagious, though feebly so.
{864} CLINICAL HISTORY.--Influenza, in individual cases, presents the
greatest variation as regards intensity, from the most trifling
indisposition to an illness of the gravest kind, terminating in death.
These variations are dependent upon--1st, the previous health of the
individual, his age, and the power of resisting depressing influences
which he possesses; 2d, the energy and the amount of the specific
cause of the disease to which he has been exposed--in other words, the
dose of the fever-producing poison; and 3d, the character of the
prevailing epidemic.
It is important to observe that cases of very great severity are
occasionally encountered during the prevalence of mild epidemics. In
every epidemic, on the contrary, a considerable part of the community
suffers from influenza in the mildest, or what has been called the
rudimentary, form. This is characterized by general malaise, an easily
oncoming weariness upon bodily and mental effort, a disinclination for
business, some inability to fix the attention, and slight mental
confusion; to these nervous disturbances are added catarrhal symptoms,
as coryza, sore throat, a tickling cough, and the like; but the
indisposition is subfebrile--it does not amount to a fully-developed
fever. Other cases present the symptoms of an ordinary attack of acute
coryza, laryngitis, bronchitis, pharyngitis, with unusual
constitutional disturbance, distressing headache, and pains in the
back and limbs. The fever in this class of cases does not range high,
yet the patients are ill enough to betake themselves to bed.
In severe cases the onset is usually abrupt. The attack begins with
shivering or a chill, or with fits of chilliness alternating with
heat. Fever is rapidly established. It is usually moderate; sometimes
it reaches a high grade. It shows a tendency to morning remissions.
Sensations of chilliness occur; they are called forth by slight
changes in the external temperature. They are often followed by
flushes of heat, and are, in many cases, attended by annoying sweats.
The febrile outbreak is sometimes preceded by intense frontal
headache, with pain in the orbits and at the root of the nose. In
other cases these pains quickly follow the chill. Sneezing, redness of
the eyes and edges of the nostrils, a more or less abundant thin
discharge from the nose, and lachrymation, now occur. In some
instances there is bleeding from the nose. The throat becomes sore;
there is a tickling sensation in the upper air-passages; a dry cough
sets in, attended by more or less hoarseness and shortness of breath.
The cough is paroxysmal, hard, distressing. It sometimes causes
vomiting, like that which occurs in the paroxysms of whooping cough.
Chest-pains, stitches in the side, frequent sneezing, loss of the
sense of smell and of taste, attend the development of the general
catarrhal manifestations.
The fever is attended by great depression, pains in the limbs, loss of
appetite, thirst, constipation, and diminished secretion of urine. The
pulse is full, but, as a rule, only moderately increased in frequency.
There is in many cases slight, or even decided, blueness of the lips
and finger-tips. The patient is distressed by restlessness and want of
sleep. At the end of four or five days the febrile symptoms decline,
at times gradually, oftener rapidly, with copious sweats or
spontaneous flux from the bowels. The fever continues, however, when
severe complications have taken place, ten or twelve days. The
defervescence is marked by {865} an increased flow of sedimentary
urine and considerable amelioration of the subjective symptoms. The
catarrhal symptoms outlast the fever two or three days, but cough and
expectoration may not disappear for some time.
With these symptoms are associated the evidences of functional
disturbance of the nervous system. There is remarkable nervous
depression; loss of strength and lowness of spirits are combined with
mental weakness, or even stupor and delirium. In some cases slight
convulsions take place. Cutaneous hyperæsthesia occasionally occurs,
and areas of burning pain in the skin are to be met with. Neuralgia,
muscle-pain, and aching referred to the bones are very common and
often severe.
In other cases abdominal symptoms are prominent, while those referable
to the head and chest are less urgent. The disease assumes the guise
of a more or less severe catarrh of the gastro-enteric mucous
membrane, with disturbance of the functions of the liver. The fever
and the peculiar nervous depression are, however, the same. Cases
likewise present themselves in which but little of the usual tendency
to localization of the catarrhal processes is to be observed; there is
fever of varying intensity, with great depression, and simultaneous
and equal implication of the head and the organs of the chest and
abdomen.
Many writers have sought to arrange the foregoing different forms of
influenza in definite categories. It would be a useless task to
reproduce their views upon the subject, or even to enumerate the
varieties that have been described. In practice, the various described
types merge so gradually into each other, and are so modified by the
individual peculiarities of the sick, and by the complications which
arise in the course of the attack in consequence of such peculiarities
or of previously existing diseases or tendencies to special forms of
disease, that, in point of fact, particular cases cannot usually be
referred to theoretical categories. Hysterical persons and those of a
nervous constitution are prone to suffer especially from the peculiar
nervous symptoms of influenza. The disease is also modified by the age
of the subject of the attack; children manifest in a high degree the
signs of cerebral congestion, while old persons are subject in a
peculiar manner to dangerous pulmonary complications, and those of a
gouty or rheumatic constitution suffer more than others from muscular
pains.
The duration of the mildest form of influenza is from two to three
days; in well-developed cases without complications convalescence sets
in between the fourth and tenth days; while severe cases with
complications last much longer, several weeks often elapsing before
recovery is complete.
SYMPTOMATOLOGY.--ANALYSIS OF THE SYMPTOMS.--For the purpose of
separate consideration it is convenient to take up the symptoms
belonging to the fever first, then those of the special catarrh, and
finally those more particularly referable to the nervous system; but
we encounter in the present state of our knowledge of the pathology of
influenza--or our ignorance of its pathology--no little difficulty in
deciding under which of these headings particular symptoms are
properly to be classed, by reason of the close interdependence of the
chief processes of the disease and the anomalies of its phenomena
viewed as a whole.
The Fever.--The fever is of the sub-continuous or remittent type,
{866} but its range is very irregular. Irregularity of temperature is
characteristic of influenza and may assume diagnostic importance.
The intensity of the fever is variable. As a rule, it is moderate or
slight; occasionally it is severe. I observed in several cases during
the epidemic of 1879 in Philadelphia an evening temperature of only
39° C. (102.2° F.). Da Costa in the same outbreak found the febrile
movement not high; the highest temperature he observed was 40° C.
(104° F.). Biermer found a temperature of over 39° C. in moderate
cases of catarrhal fever, and does not doubt that under certain
transient conditions the temperature may reach the height of that of
pneumonia or typhus. In weakly persons and the aged the fever is
adynamic.
The pulse has no constant characters. Its frequency is moderately
increased; it is apt to be less forcible than in health, is generally
compressible, sometimes full, often irregular, changing in character
in the course of a few hours.
The urine is usually diminished; sometimes its secretion is
temporarily suppressed; as a rule, it shows little change, and is
rarely, as in other fevers, concentrated and high-colored. It deposits
on cooling a sediment of urates, which toward the close of the fever
is often very abundant. The defervescence is in many instances
attended by a copious secretion of urine. Albumen is not present
except as a result of some complication.
At first the skin is hot and dry; later, frequent sweats occur;
sweating generally attends the febrile remissions and the
defervescence not rarely sets in with copious, acid, ill-smelling
sweats. In some cases a tendency to sweat shows itself early and
continuous throughout the attack. Sudamina occur in great numbers.
The face is often flushed, and irregular mottlings of the skin,
especially upon the neck and chest, have been frequent in some of the
epidemics. An outbreak of herpes about the lips is occasionally seen.
Disturbances of the digestive tract are more or less prominent in
almost all cases. Only in a rudimentary and sub-febrile form are they
absent. In many cases they are such as are usually seen in febrile
disorders--namely, loss of appetite, thirst, impaired taste, pasty
tongue, tenderness in the epigastrium, and constipation. Nausea and
vomiting sometimes usher in the attack. In other cases (the so-called
abdominal form) all the above symptoms are more severe, and diarrhoea,
colicky pains, and vomiting are superadded. In certain epidemics the
intestinal catarrh has shown a tendency to run into dysentery.
The expression of the countenance is changed, in part by the
appearance characterizing an ordinary attack of coryza of considerable
or great severity, and in part by anxiety and depression. It is pale.
Where the pulmonary catarrh is excessive and dyspnoea great the lips
become bluish. The facies sometimes suggests that of typhoid fever.
The Catarrh.--A more or less extensive hyperæmia of the mucous
membrane of the respiratory tract is invariably present, and may be
said to characterize the disease.
There is cold in the head, more severe in most cases than ordinary
simple coryza. The eyelids are swollen and reddened, there is
lachrymation, sneezing is frequent, and the discharge from the nose is
abundant. Epistaxis is not rare. Sore throat, with tickling sensations
and difficulty {867} in swallowing, is due to inflammation of the
pharynx and neighboring parts. In many instances the catarrhal
symptoms are due to a pharyngitis and tonsillitis only, the lower
air-passages escaping. Hoarseness is common.
Cough is a prominent symptom. It is apt to be frequent and
distressing--sometimes paroxysmal from the beginning of the sickness,
almost always so at some period of its course. Its spasmodic character
in some of the older epidemics led to the confounding of epidemic
catarrhal fever with whooping cough. It is apt to be worse toward
evening and at night, but the sick are often tormented day and night
by the loud racking cough. It often leads to vomiting, and by its
violence and persistence gives rise to pain and soreness in the
muscles of respiration (myalgia), and occasionally to hernia. It is at
first dry or attended with a scanty muco-serous expectoration; later
on the sputa become opaque and muco-purulent, and in consumptive or
full-blooded persons or those having mitral disease they are sometimes
streaked or mingled with blood. Toward the close of the attack the
cough becomes less urgent and loses its spasmodic character. In some
epidemics cough is not a prominent symptom, and a few cases are
encountered in most epidemics in which well-developed influenza runs
its course without unusual, peculiar, or excessive cough. If the cough
be due to bronchitis, we find on auscultation the physical signs of
that affection. They are of course wanting when it is due simply to
laryngo-tracheal irritation. Hence we frequently detect sonorous and
sibillant or mucous and subcrepitant râles upon both sides of the
chest in the course of the attack, as in non-epidemic acute
bronchitis; and, on the other hand, cases occur where the auscultatory
signs are but little or not at all altered from those of health. It is
scarcely necessary to add that there are no special physical signs
that can be regarded as diagnostic of influenza.
Many patients suffer from dyspnoea. Although due in some instances to
complications, it occurs with remarkable frequency in those in whom
none of the objective signs of any pulmonary lesion can be discovered.
It is here of nervous origin. Graves assumes a direct disturbance in
the function of the vagus as its cause. This view is sustained by the
observation that the dyspnoea is now and then intermittent, or shows
rhythmically recurring remissions, which are unattended by alteration
of the physical signs. To Biermer it appears more probable that the
congestions so common in influenza, not attended by marked physical
signs until they lead to oedema, are to be regarded as the cause of
the dyspnoea. It varies greatly in intensity. In many patients it goes
on to marked oppression, great shortness of breath, precordial pain,
and the like. In certain epidemics orthopnoea and suffocative attacks
were very common. Stitches in the side and pain under the sternum are
observed without appreciable physical signs.
Symptoms Referable to the Nervous System.--Great prostration of
muscular strength is a very early symptom, and constitutes, in most
epidemics, one of the remarkable features of the disease. Patients
from the onset feel extremely weak, and are exhausted by the slightest
bodily effort. The ordinary strength is not regained until
convalescence is far advanced.
Headache is a constant symptom. Severe frontal pains are scarcely
{868} ever absent. They extend across the brow and deeply about the
orbits and at the root of the nose, having their seat in the
Schneiderian mucous membrane and its prolongations lining the frontal
sinuses and the nasal ducts. Sometimes the pain is referred also to
the region of the antrum of Highmore and to the Eustachian tube and
the middle ear. It occasionally extends over the whole head. Cutaneous
hyperæsthesia of the head and neck and stiffness of the neck-muscles
are also met with. The headache is often most intense; it lasts
commonly till the end of the attack, and may even outlast it. It
increases in severity with the fever and mental agitation toward
evening. The occurrence of epistaxis affords some relief.
Among the more constant symptoms of influenza are very severe pains in
the limbs. Patients experience sensations of soreness and bruising,
such as follow the most severe and unaccustomed muscular effort. Dull,
tearing, and burning pains are felt sometimes in particular muscles or
tendons; sometimes they are diffused over the whole body. Distressing
pains of a dragging or boring character in the loins and calves of the
legs are complained of. These pains are neither relieved nor
aggravated by gentle movement or by moderate pressure. A sense of
contraction of the chest and precordial distress also occurs, and
stitches in the side (pleurodynia), substernal pain, and pains in the
throat and nape of the neck are common. When the attack is severe the
patient is usually restless, sleepless, and anxious. Dizziness and a
tendency to faint occur on rising, particularly in women. Mild
delirium is not uncommon, but the more intense forms are occasionally
observed. Active delirium was thought to be a mortal symptom in some
of the older epidemics.
The inability to sleep bears no direct relation to the intensity of
the fever. It is seen in some cases where fever is slight or even
absent.
Somnolent states also occur. Great hebetude and torpor have marked
some epidemics. That of 1712 was called the sleepy sickness, by reason
of the prevalence of these symptoms.
In grave cases painful muscle-cramps, subsultus tendinum, twitchings
of particular muscles, and tremblings of the hands occur.
The mental power is enfeebled, and the acuteness of the special senses
is diminished.
COMPLICATIONS AND SEQUELS.--The most important complications of
influenza are inflammatory diseases of the lungs. The hyperæmia and
intense bronchitis already described as occurring in the severer cases
cannot properly be looked upon as complications. They constitute
rather essential processes of particular forms of the disease. But
capillary bronchitis, catarrhal pneumonia, and less frequently
croupous pneumonia, arise as complications in the course of the
disease. Satisfactory statistics are wanting, but Biermer estimates
that from 5 to 10 per cent. of the whole number of patients suffer
from inflammatory lung-complications, and holds that the bloodletting
so frequently practised by the older physicians was due to a desire to
combat inflammation. The comparative frequency of chest complications
in different epidemics varies greatly, but the estimate of Biermer may
be accepted as an approximate average.