CONTENTS.

EPIDEMICS—

QUARANTINE—

CONTAGION—

APPENDIX.

THE COMMON NATUREOFEPIDEMICS.

THE COMMON NATURE

EPIDEMICS.

Some account of the structure and functions of the human frame, of the action of physical agents on this wonderful machinery, and of the principles which relate to Individual, as well as to Public Health, ought to form a part of elemental education. There is a growing conviction that the necessity for such knowledge is not restricted to the physician; that it is essential also to the educator, the mother, the nurse, and indeed to every one who would enjoy, together with the due development of his physical, intellectual, and moral nature, the full term of the boon of life.

The main causes which shorten and embitter human life, as far as that unhappy result depends on the disturbance of health, are within our own control. There is the closest connection between the knowledge we have acquired of the physical conditions on which the life and health of individuals and communities depend, and on our command over those conditions. Every fact we have learnt respecting the great laws of nature, on our conformity to which our very existence depends, has taught us that the circumstanceswhich produce excessive sickness and early death are preventible.

The character of Pestilence which gave it its great power and terror—that it walketh in darkness,—is its character no longer. Its veil has fallen, and with it its strength. A clear and steady light now marks its course from its commencement to its end; and that light places in equally broad and strong relief its antagonist and conqueror—Cleanliness.

The term Epidemic has become a popular one. It is derived from two Greek words, which signify “upon the people—prevalent among the people”—diseases which, at one and the same time, prevail extensively among large masses of the people.

Recently these diseases have received another name, which is also becoming familiar—“Zymotic,” from a Greek word, which signifies to “ferment,” as if the efficient cause of these diseases, whatever it may be, acts in the manner of a ferment.

Epidemic diseases, though called by a common name, present great differences in their external characters. Plague, Yellow Fever, Cholera, Small-Pox, Typhus, Scarlet Fever, Influenza, present characters so definite and special, that they have been naturally regarded as distinct diseases, and they really are so different as to render it desirable, for many reasons, that each should be discriminated and denoted by its proper name. Amidst this great diversity in form, however, they present very striking resemblances, of which the following are generally recognized:—

1. Epidemics resemble each other in being all fevers. They all exhibit that particular assemblage of symptoms which from time immemorial it has been agreed to denote by the term Fever.

This is as true of the great Epidemics of former times as of those which prevail in our own.

The so-called Black Death of the 14th century was a fever—an aggravated form of the Oriental or Bubo-Plague; in which there occurred, in addition to the ordinary symptoms of that dreadful disease, effusions of black blood, forming black spots on the arms, face, and chest. From this circumstance it derived its name. These effusions on the external surface of the body were accompanied by profuse and mortal discharges from the internal organs.

The Oriental Plague, the great devastator of Europe in former times, and still the scourge of some portions of it, is a fever characterized by specific glandular inflammation.

The Sweating Sickness of the 15th and 16th centuries was a fever, with symptoms of acute rheumatism, attended with a fœtid perspiration which poured from the body in streams. “Suddenly,” says Hollingshed, “a deadly burning sweat assailed their bodies and distempered their blood, and all, as soon as the sweat took them, yielded the ghost.”

The Cholera of modern times is a fever, which appears in its true character when the first stroke of the disease does not prove fatal, and time is allowed for the full development of its successive stages.

The common Epidemics of the day—Ordinary as distinguished from Extraordinary Epidemics—typhus, scarlet fever, small-pox, measles,—are so universally recognized as fevers that the popular notion of fever is derived from the external characters which these maladies present.

2. Epidemics resemble each other in the extent of their range. Ordinary diseases attack single individuals, and if, from season or other causes, several cases occur simultaneously, they are still isolated and scattered. They never prevail at the same time among several members ofa family, or among the inhabitants generally of a court, street, or town. Epidemics, on the contrary, derive their name from their attacking large numbers at once.

The great Epidemics of all ages have been strikingly characterized by their wide-spread course. The Black Death extended from China to Greenland, and desolated in its course Asia, Europe, and Africa.

The Bubo-Plague of the middle ages often extended beyond its proper seat. In the 15th century it spread seventeen times over different European countries, and extended to the most distant northern nations.

The Sweating Sickness prevailed simultaneously or in rapid succession over England, France, Germany, Prussia, Poland, Russia, Norway, and Sweden. “It extended,” say the chronicles of the day, “like a violent conflagration which spread in all directions; yet the flames did not issue from one focus, but rose up everywhere as if self-ignited.”

The Influenza of the middle ages took a range which may be said to have been universal. In our own day we have seen the same disease attack almost every family, in nearly every city, town, and village; spread within a short period over the whole of Europe, and then extend through the vast continent of the New World.

Cholera traverses the earth in zones, spreads with equal facility through tropical and polar regions, and attacks alike the seats of civilization and the huts of the slave and the savage.

3. Epidemics resemble each other in the rapidity of their course. Sometimes, indeed, they begin slowly, advance haltingly, and gather strength in silence. For some time they give so little indication of their power that the apprehension of their presence is very constantly regarded as a “false alarm.” Now and then, here and there, they strike a sudden and mortal blow; but it is only an individualthat falls. After a considerable interval, perhaps at a great distance, another blow is struck; and then one by one, another and another, until at last the fact becomes too manifest to be doubted or denied, that two victims have been seized in one family—several in the same street—three or four on the same day, in distant parts of the town, or in the adjoining town, or it may be in towns separated from each other by the distance of hundreds of miles. At length the terror-stricken nation, startled from its fondly cherished security, sees no place safe from the Plague. When, however, the causes are intense, it may break forth quite suddenly, and spread with astonishing rapidity.

In 1831, when Cholera first appeared in Cairo, it extended within the space of five days over the whole of Lower Egypt, desolating simultaneously all the towns and villages of the Delta.

In 1832 it leaped at one bound from London to Paris, and when once there, spread in five days over thirty-five out of forty-eight quarters of the city.

When Influenza broke out in London in 1847, it spread in one day over every part of the metropolis, and upwards of 500,000 persons suffered from the malady.

4. Epidemics resemble each other in giving distinct and unmistakeable warnings of their approach. These warnings consist of two events: first, the sudden outbreak and general spread of some milder epidemic; and, secondly, the transformation of ordinary diseases into diseases of a new type, more or less resembling the character of the extraordinary disease at hand.

It is a very singular fact that both in the middle ages, and in modern times, the lesser Epidemic which has generally preceded and pre-announced the coming of the greater, is Influenza.

The history of European Epidemics from the 14th centurydownwards, shows that whenever a new Plague was at hand, destined to become truly European, it was preceded by a sudden outbreak of Influenza, as general as it was violent. This is exemplified with singular uniformity in the Epidemics of the 16th century—the severest epidemic period on record. It is most remarkable that in our own day the first visitation of Epidemic Cholera was preceded by an outbreak of Influenza which resembled, in the most minute particulars, the violent and universal Influenza that ushered in the mortal Sweating Sickness Epidemic of 1517.

So again, on the second visitation of Cholera, in 1848, it was preceded, as we have just seen, by the universal Influenza of 1847.[3]

3.It may be remarked that for some time prior to the Cattle Plague in the autumn of 1865, the disease calledpleuro-pneumoniahad extensively prevailed among the herds throughout the country. [Ed.]

The second circumstance, and a most instructive one it is, premonitory of the advent of a great Epidemic, is a general transformation of the type of ordinary diseases into the characteristic type of the approaching pestilence. Sydenham gives a graphic description of such a transformation in the character of the fevers and inflammatory diseases prevailing in London some months before the outbreak of the Great Plague. He states that this change consisted in an approximation, in several striking features, of the general type of disease, to the distinguishing characters of the Pestilence which had not yet appeared, but was close at hand.

In 1831, in the wards of the London Fever Hospital, I observed and recorded a precisely similar change in the general type of the fevers in London, six months before the first visitation of Cholera. Anterior to that period, fever in London, for a long series of years, had been essentially an acute, inflammatory disease, for which bloodlettingand other depleting remedies were indispensable. At this period it ceased to be an inflammatory disease; it became a disease of debility, in which no one could think of bleeding; and so closely did the prevailing fever now put on the general character of the approaching plague, which was as yet six months distant, that the fever into which those Cholera patients fell, who were not killed by the first stroke—the consecutive fever, as it was afterwards called—could not be distinguished from the primary fever in the wards of the Hospital when Cholera was at its height, which had appeared there for the first time six months previously, and which has never disappeared since.[4]

4.This was written in November, 1855.

It is further very remarkable that the Professors of Veterinary Medicine and Surgery in London noted at the same time a similar change in the type of the diseases of the lower animals—horses, cows, sheep, and all domestic creatures;—a change requiring a similar modification of the remedies which they had been in the habit of using.

5. A further character of great Epidemics, partly arising from the last, is this:—they are actually present and in operation some time before they assume their distinct and proper form. Sometimes, indeed, the very first cases are most intense and characteristic, but at others they are scarcely to be distinguished from the severer attacks of ordinary disease of a like nature. Hence doubt is sometimes reasonably entertained of their true character. When at length increasing numbers leave no doubt of the actual presence of the dreaded malady, the first announcement of it is always received with incredulity and sometimes with resentment; and so it is that Epidemics always take a country by surprise—burst suddenly on an unprepared people, who wilfully shut their eyes against the plainestevidence, as if they would avert the event by denying its existence.

6. Again, Epidemics resemble each other in the uniformity of their course. They present, with great regularity, periods of comparative quiescence and activity—periods of well-marked increase, culmination, and decrease.

7. They further resemble each other in the manner of their migration. They advance by leaps. On breaking out in a locality they soon come to their height, decline, and disappear. Then they attack another locality; here they pass through precisely the same process as before, and proceed to a third, fourth, or fifth district, and so on. Sometimes indeed they localize themselves on the same spot for a considerable period, and then several places may be simultaneously affected; but for the most part a large city may be regarded as a cluster of towns, through the several districts of which epidemics advance as if they were proceeding from one town or village to another. Hence the duration of an epidemic in a place is generally proportionate to its size. The several localities attacked being visited in succession, a space of time is required to spread through the whole of them proportionate to the magnitude of the town.

8. Epidemics resemble each other in the periodicity of their return.

On its first visitation (1485) the Sweating Sickness spread over the whole of England in the course of one year, when it disappeared.

After an interval of twenty years it broke out a second time quite suddenly (1505); revisited nearly all the seats of its former ravages, and again disappeared at the end of six months.

On its third visitation (1517), after an interval of eleven years, it again finished its course within six months.

Its fourth visitation (1528) was repeated after a furtherinterval of precisely eleven years. Such was its violence on this occasion, that the historians of that day designate this period by the significant name of the “Great Mortality.” It drove Henry VIII. from London, destroyed several of the most distinguished persons of the Court, impressed the nation, from the monarch to the peasant, with an awful feeling of the uncertainty of life, continued its destructive course for its accustomed period of six months, and then again disappeared.

From this to its fifth and last visitation, twenty-three years elapsed (from 1528 to 1551.) It then broke out with unmitigated fury, spread once more over the whole of England, ceased within six months, and from that period has never reappeared in any country.

The Oriental Plague of the middle ages returned with a like periodicity; and so it does at the present day in the countries in which it maintains its ancient reign. It recurs with much regularity about every ten years.

The Fever Epidemics of the metropolis return pretty constantly about every ten or twelve years.

The Irish Typhus Epidemics have recurred nearly decennially for the last 150 years.

Epidemic Cholera, on its first visitation, ravaged Great Britain for a period of fifteen months. It then wholly ceased; after an interval of sixteen years it again broke out, and pursued its former course for the same exact period of fifteen months, and then ceased.

Within the brief interval of only five years, it last year (1854) accomplished its third visitation. It now protracted its stay for a period of seventeen months; coming sooner and staying longer.

9. Again, Epidemics resemble each other in the brevity of the space that intervenes between the attack and death.

The Black Death was often fatal on the first day of the attack—generally on the third or fourth. In England itwas sometimes fatal within twelve hours, and frequently in two days, particularly when spitting of blood or any other form of hœmorrhage was amongst the early symptoms.

The violent inflammatory fever which characterized the Sweating Sickness, generally ran its course in a few hours; in severe cases, indeed, the crisis was always over within a day and night, but it often proved fatal in six hours.

In our own day we have witnessed many instances in which Epidemic Cholera was fatal within twelve hours. I have known several in which the fatal event followed in ten hours, the patient having been within an hour of the dreaded attack inapparenthealth.

In all great epidemics the protraction of the disease beyond three or four days is a favourable omen. One of the objects in the treatment of the sick is to gain time. If Nature’s first violent effort to expel the enemy that has taken possession of the system, does not destroy life, the vital powers rally, and the frame often survives the storm.

10. Lastly, Epidemics resemble each other in being produced by the same causes. The whole tenor of experience shows that whatever produces an especial liability to one epidemic, produces a similar liability to every other.

The Causes of epidemics, as of all other diseases, are divided into two classes,—the predisposing and the primary. The predisposing causes are those circumstances which bring the body into a fit state for the action of the primary. The primary cause is the agent which directly and immediately excites the disease.

If a number of persons, in an ordinary state of health, say a hundred, are exposed to the primary cause of any epidemic—to the poison of Cholera for example—probably not more than ten would be seized with the disease. Why do the ninety escape? The poison, by the supposition, encompasses and acts upon all alike: why do ten onlysuffer? Suppose these same hundred persons took a large dose of arsenic, or an over-dose of chloroform, not only would not one in ten escape, but every individual would certainly perish.

It is conceived that the primary cause cannot take effect unless the system be in a state of susceptibility to its action; that there is in the body an innate power of resistance to all noxious agents of this kind, rendering it, when in full vigour, invulnerable to them; that there are certain circumstances which weaken or destroy this resisting power, and which even impart to the body a peculiar susceptibility to the influence of such agents—and these circumstances are called predisposing causes.

The predisposing causes of epidemics may be divided into two classes—External and Internal. The external are those which vitiate the atmosphere; the internal are those which more immediately vitiate the blood.

The vitiators of the atmosphere include overcrowding, filth, putrescent animal and vegetable matters of all kinds, exhalations from foul cesspools, sewers, rivers, canals, ditches, marshes, swamps, &c. Causes of this class are also calledlocalizing, because they favour the generation and spread of epidemics in the localities in which they abound.

The causes which more immediately act from within are those which either directly introduce pernicious matters into the interior of the body, in the shape of foul water or putrescent food; or which indirectly accumulate noxious matters within the system, by impairing the action of the excretory or depurating organs whose office it is to maintain the blood in a state of purity, by removing out of the system substances which having served their purpose have become useless and pernicious.

The earnest attention which has been recently directed to the first class of causes has led to an advancement inthe science of prevention, the importance of which it is impossible to over-estimate.

To give only one illustration of the action of a predisposing cause, I select as my example,Overcrowding.

The Statistical Society of London some time ago appointed a Committee of its Council to make a house-to-house examination of the parish of Marylebone, with a view to ascertain how many families in the parish occupied a single room as a living and sleeping room. In the course of this inquiry, one of the examiners came to a house in which there was one remarkable room. It was occupied not by one family only, but by five. A separate family ate, drank, and slept in each of the four corners of this room; a fifth occupied the centre.

“But how can you exist,” said the visitor to a poor woman whom he found in the room (the other inmates being absent on their several avocations), “how can you possibly exist?”

“Oh, indeed, your honour,” she replied, “we did very well until the gentleman in the middle took in a lodger.”

I see every day in the wards of the Fever Hospital the consequence of taking in such lodgers. An epidemic shows it not more truly, but more strikingly.

Within the walls of an establishment for pauper children at Tooting, in 1849, there were crowded 1395 children. Little more than one hundred cubic feet of breathing space was allowed for each child, 500 being the smallest compatible with safety. One night Cholera attacked sixty-four of these children; 300 were attacked in all. Within a week 180 perished.

In the Workhouse of Taunton there were 276 inmates. In some of the rooms the breathing space was not more than sixty-eight cubic feet. Cholera swept away 60 of these inhabitants in less than a week.

In the County Jail of this same town, the breathingspace allowed to each prisoner ranges from 819 to 935 cubic feet. Not a single case of cholera, nor even of diarrhœa, occurred among the prisoners in this jail.

The town’s people also escaped, while in the overcrowded workhouses, 22 per cent. of the total number of the inhabitants were swept away.

In the village of East Farleigh, near Maidstone, 1000 persons were assembled for hop-picking. They were lodged in sheds, and had about eighty cubic feet for breathing space: in a few days diarrhœa became universal among them: ninety-seven were attacked with cholera, and forty-six died. In the same village, at the same time, under another employer who had provided proper accommodation for his labourers, there was a complete immunity from the epidemic.

I could add cases of the like kind without number. I could show that animals are affected by this cause of disease no less than men; that horses overcrowded in stables die of glanders; dogs in overcrowded kennels die of distemper; sheep overcrowded in ships, even during a short passage from one country to another, die in great numbers of febrile diseases:[5]results which prove the operation of a general law of nature. I could adduce equally decisive examples of the action of each of the principal external predisposing causes just enumerated.

It has been often said that we cannot tell the difference between the air of the mountain-side and that of the crowded hospitals and fever-nests of towns. If it were so, it would be sufficient to say, Life is a more delicate test than Chemistry. But it is not so. The impurities in these pernicious places can be detected by chemical analysis, and examined as readily as the constituents of the atmosphere itself.

5.It has been alleged that the Cattle Plague owed its existence to these among perhaps other kindred causes, and human Epidemics have frequently been preceded or accompanied by a murrain among Cattle. See p.7, and Boa Vista fever,pot.[Ed.]

The moisture in the air of a crowded room may be condensed by ice. It condenses indeed spontaneously on the walls and windows, and on all surfaces, and may be collected in sufficient quantity for examination and experiment.

If a portion of this deposit be put on a piece of platinum and burnt, a strong odour of organic substance is given off, and a quantity of charcoal remains. If the deposit be allowed to stand for a few days, it forms a solid, thick, glutinous mass, having a strong odour of animal matter. If examined by a microscope, it is seen to undergo a remarkable change. First of all, it is converted into a vegetable growth, and this is followed by the production of multitudes of animalcules,—a decisive proof that it must contain organic matter, otherwise it could not nourish organic beings.[6]

6.See the interesting experiments of Dr Angus Smith, on the Air and Water of Towns, “Report of the British Association for the Advancement of Science,” p. 16,et seq.

At every expiration the lungs pour a portion of organic matter into the surrounding atmosphere; at every moment the skin does the same. This matter is the dead portion of the body, which it is one of the special offices of these depurating organs to remove out of the living system as useless and pernicious.

It is indeed pernicious, for it is an animal poison, more concentrated in this than in any other form of excrementitious matter, since in other excretions the noxious particles, in their transmission out of the body, are diluted with other substances, but as they issue from the lungs and skin, they are in a great degree undiluted. Ventilation and cleanliness prevent this matter from accumulating, and render it innoxious. But it collects in large quantities on the furniture and walls of dirty houses, and is the main cause of the disagreeable smell of the rooms in which it abounds. In some instances the walls are coated with it.It was so in one particular building in which, during a local epidemic outbreak, twelve persons were attacked with cholera, and four died.

From recent chemical and microscopical examinations of the air of some crowded and filthy localities in the metropolis, it appears as a general result, that decomposing organic matter is always contained in such air,—the never-failing presence of animalcules testifying its existence, and their number and size indicating its amount.

Imagine the state of the atmosphere in the dormitories of the Tooting children: in the sixty-eight cubic feet of breathing space of the inmates of the Taunton Workhouse; in the eighty cubic feet of the Kentish hop-pickers; in the four corners and centre of the five-family room.

Conceive the state of the atmosphere in this room at night; all the members of the several families, collected; every breath of external air excluded; the windows, and perhaps even the chimney, carefully fastened up. This stagnant and poisoned air, breathed over and over again by every individual for seven or eight hours continuously; respiration, the special and admirable apparatus which nature has constructed for purifying the blood, thus made the very means of corrupting it. I have known from two to three cases of typhus produced nightly, for a fortnight together, in a room of this description, by sleeping in it for a single night! Can we wonder at the generation of typhus in such a room inordinaryseasons! Can we wonder at the spread and the havoc of an epidemic in it inepidemicseasons?

But besides the contamination of the air by external causes, it is conceived that the atmosphere itself undergoes natural changes which predispose it to the development and spread of epidemics. From time immemorial, the popular belief has been that such changes do take place,and that they manifest themselves by unmistakeable signs.

Among such signs may be reckoned,—a disturbance of the regular and ordinary condition of the atmosphere; an inversion of the seasons—summer in winter, and winter in summer; long-continued drought succeeded by torrents of rain, causing rivers to overflow, and the seed to rot in the earth; cloud, mist, fog, favouring excessive dampness, under the influence of which spring up inordinate growths of the lower species of plants, producing mouldiness, and the blood-spots, and other coloured vegetation that adhere to houses, and household furniture, and wearing apparel, and personal ornaments, and the person itself; under which also, fostered by a steadily elevated temperature, spring into being and activity, myriads of the lower tribes of animals—locusts, caterpillars, flies,[7]frogs, covering the face of the earth, and devouring every green thing that the deluge of rain had left; and, as the sequence of these antecedent conditions, dearth and famine, closing the long series of the year’s calamities. Such, in all ages and countries, have been the recognized portents and precursors of a coming year of pestilence.

7.During the autumn following the extraordinary summer of 1865, and in which the Cattle Plague appeared, there was a very marked preponderance of insect life as compared with ordinary seasons. It is asserted by Mr Mc Dougall, of Manchester, that no case of this plague is known to have occurred where his disinfectant, which arrests decomposition, had been freely applied to and about the cattle. [Ed.]

And there is truth in this.

It is quite certain that such atmospheric changes do take place, and prepare the way for pestilence. It is quite certain that there is an epidemic meteorology. This epidemic condition of the atmosphere is at length coming within the range of science. The first step towards this result, which promises to be of the highest practical value, we owe to the well-devised and patient observations of Mr Glashier, continued through the three recent Cholera epidemics.

Among other important facts, he has determined that there is—1. An increased pressure of the atmosphere, greatest at the worst period of the epidemic.

2. An increased density of the atmosphere, not arising from an increase of watery vapour; for,

3. The quantity of water in the air was 1/20th less than the average, at the same time that the mean weight of a cubic foot of air was 2 grains above the average.

4. An unusual alternation of heat and cold, yet the heat predominating to such an extent that in particular localities it rose as much as from 2° to 8° above the average. These excesses were most striking at night, particularly in the parts of London on a level with the Thames, where the night temperatures ranged from 7°, 8°, 9°, and 10° above the temperature of the country, and even of the suburban districts. These temperatures were highest, especially the night ones, when the mortality was greatest; and the mortality was greatest where the temperatures were highest.

5. A remarkable increase above the average in the temperature of the water of the Thames. From a long series of observations it had been found that the normal temperature of the Thames is 51.7°. During the prevalence of the epidemic it rose to 60°, 66°, and once to 70°. At this temperature the “simmering” water must have poured enormous quantities of vapour into the surrounding atmosphere; not the pure vapour of water, for that cannot arise from a river which is the recipient of the foul contents of all the sewers and cesspools of the metropolis. In some instances there was an excess of 20° of the temperature of the water above that of the air. For twenty-eight continuous nights during the height of the epidemic, the average excess exceeded 16.5°.

6. An unusual prevalence of haze, mist, and fog; the fog being sometimes so dense that London could not be discerned from Greenwich.

7. An extraordinary stillness and stagnation of the air, both by day and night. Sometimes in the low-lying districts not a breath could be observed. Even when at more elevated stations the wind was moving with a force of 1 lb 7 oz., the pressure was only ¼ lb in the heart of London.

Wind is the ventilator of nature. Artificial ventilation, as far as it is successful, is an imitation of nature’s process. It is stated on undoubted authority (Maitland’s History of London) that for several weeks before the Great Plague broke out in London, there was an uninterrupted calm, so that there was not sufficient motion of the air to stir a vane. Baynard, a contemporary physician, confirms this fact. The like circumstance is mentioned by Diemerbroeck in giving an account of the plague at Nimeguen. At the period when the last plague visited Vienna, according to Sir Gilbert Blane, there had been no wind for three months. The terrific outbreak of the cholera at Kurrachee was preceded for some days by such a stagnation of the atmosphere that an oppression scarcely to be endured affected the whole population. It is obvious that calms must favour the accumulation and concentration of effluvia from every source from which they arise.

8. A general deficiency in the tension of common positive electricity.

9. A deficiency of one fourth of the rain-fall for the year. During 118 consecutive days there was scarcely any rain, and not a single drop for 18 days at the period of the highest mortality.

10. A total absence of ozone at all the stations near the river, while at stations of high elevation it was of general occurrence.

These observations relate particularly to the epidemic of 1854, which was more carefully watched than the two former; but the results are similar for each.

“The three epidemics,” says Mr Glashier, in summing up the results of his inquiry, “were attended with a particular state of atmosphere, characterized by a prevalent mist, thin in high places, dense in low. During the height of the epidemic, in all cases, the reading of the barometer was remarkably high, the atmosphere thick; and in 1849 and 1854 the temperature above its average. A total absence of rain, and a stillness of air amounting almost to calm, accompanied the progress of the disease on each occasion. In places near the river, the night temperatures were high, with small diurnal range, with a dense torpid mist and air charged with the many impurities arising from the exhalations of the Thames, and adjoining marshes; a deficiency of electricity, and, as shown in 1854, a total absence of ozone, most probably destroyed by the decomposition of the organic matter with which the air in these situations is so strongly charged.

“In both 1849 and 1854, the first decline of the disease was marked by a decrease in the readings of the barometer, and in the temperature of the air and water; the air, which previously had for a long time continued calm, was succeeded by a strong S. W. wind, which soon dissipated the former stagnant and poisonous atmosphere.”

We knew before that such influences were in operation, but they had not been weighed and measured. We now know definitely something of an epidemic atmosphere, and the information obtained is most significant; for it shows that the several meteorological changes that take place during the prevalence of an epidemic concur to produce a heavy, warm, moist, and stagnant atmosphere, with disturbed electricity: conditions highly favourable to the decomposition of organic matter.

Under the influence of such an atmosphere, over the moist and warmed surface of every filthy place, over the entire mass of all accumulations of filth in streets, lanes, andcourts, and within and about houses, and over the heated surface of all foul water, decomposition goes on with the utmost activity, and the products are poured into the stagnant air.

Against such products the human body has no defence. The lungs admit whatever is brought to them—poisonous and salubrious substances alike. They are guarded by none of those protective contrivances which we see in some other parts of the body. Whatever is capable of suspension in the respired air passes with it directly into the current of the circulation, and when once there, is carried with astonishing rapidity into the very substance of the vital organs.

From the quantity of air which the lungs receive, some conception may be formed of the amount of obnoxious matter which may be introduced into the system through these portals.

At each inspiration there enter the lungs of an ordinary-sized person about 20 cubic inches of air. There are 20 respirations in a minute: 400 cubic inches of air must therefore enter in one minute; 14 cubic feet in one hour, and 366 cubic feet, or 36 hogsheads, in one day. To meet this the heart sends into the lungs at each contraction two ounces of blood; there are 75 pulsations in a minute, during which 150 ounces are propelled into the lungs; a quantity which gives 562 pounds in one hour and 24 hogsheads in 24 hours.

The main purpose for bringing these enormous quantities of air and blood together, with such velocity, is to provide for the enormous waste which is caused by the rapid and unceasing mutation of organic matter. The activity of an organ is sustained at the expense of the matter of which it is composed. No thought passes through the mind, but an equivalent portion of the substance of the brain is consumed; no nervous current flows along thenervous conducters, but a corresponding portion of nervous tissue is used up; no muscular movement, no glandular secretion, takes place without a proportionate waste of muscle and of gland. What must be the amount of supply required to meet this waste, when able-bodied men employed in their ordinary labour lose from 2 lbs. to 5 lbs. and upwards of their weight twice a day.[8]Some physiologists of eminence have estimated that in order to supply that waste, there passes in the course of every 24 hours as much fluid through the thoracic duct[9]as equals the whole quantity of blood in the body.

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