1. In the minor form of the disease spontaneous swellings of the glands occur, chiefly in groins and armpits, but also in neck or other parts, which either undergo resolution or suppurate. There is a certain amount of fever; the temperature is rarely high, but has been known to be 104° Fahr. The duration of the disease is ten to twenty days usually, but may be eight weeks, for most of which time the general health is little impaired and the patient able to go about as usual. It rarely, if ever, causes death, the only fatal case at Astrakhan in 1877 having been so through a complication. The disease is not obviously contagious; whether it is propagated by infection or not is unknown. It is possibly rather of a miasmatic character. This form of disease has sometimes preceded or followed severe epidemics, as in Mesopotamia (Irak) on several occasions, 1873-78, and in Astrakhan, 1877; its importance in relation to the origin of plague has only lately been appreciated.

It might be expected that gradations would be found connecting this form with the severe epidemic form; but this appears to be not usually the case, the latter form appearing somewhat suddenly and abruptly. Hence the minor form has probably often been regarded as a distinct disease, even when observed in plague countries.

2. As regards pestis major, or severe plague, the symptoms appear to have been nearly the same in all great epidemics for several centuries, if not for two thousand years, but will be best given from modern observations, such as those of Surgeon-Major Colvill, Dr Cabiadis, and others in Irak, and recent observers in India. The early symptoms are sometimes like those of ague (shivers, often long continued, and pains in the limbs), but combined with nervous symptoms. The patient becomes distracted, tosses about in constant fear of something he cannot describe, has a difficulty in understanding the questions put to him, and is slow in answering. He is often described as staggering like a drunken man. There is severe headache, intense thirst, and severe pain in the epigastrium. The eyes are red and turbid; the tongue swollen, dry, and fissured, sometimes black, sometimes remarkably white (Colvill). This condition may pass into coma even before fever sets in. In other cases bilious vomiting is the earliest symptom. The fever which sets in may last twenty-four to thirty hours, or more. The temperature maybe 100° to 107° Fahr., or even higher; but in the most rapidly fatal cases there may be little or no fever. Generally there is obstinate constipation, but sometimes diarrhoea. Besides these symptoms there are certain special ones especially characteristic of plague.

(a) Buboes or glandular swellings are observed in all except very rapidly fatal cases. They occur in 45 or 50 per cent, of the cases in the groin, in 35 per cent, in the axilla, also less frequently in the neck or other parts. These swellings may occur before the fever, simultaneously with it, or some hours after it has set in. A sudden pain like that of a stab is felt in some region of the body, which has given rise to the superstition that the unfortunate victim was wounded by the arrow of an invisible demon,—a belief recorded in Constantinople in the 6th century, and said still to survive in Mohammedan countries. The buboes may suppurate, and free discharge of matter from them has in all times been held to be a favourable sign and conducive to recovery.

(ό) Carbuncles were observed in about 2⅜ or 3 per cent, of the cases in recent epidemics in Irak. They are always an unfavourable sign.

(c) Petechiae or haemorrhagic spots on the skin have always been regarded as signs of the worst omen. Under the name of “tokens” they were considered in the English epidemics of the 16th century as the infallible signs of approaching death. “They appear generally only a few hours before death” (Colvill). Hodges (1665) noticed hardness which showed the existence of haemorrhage under the skin. The skin is sometimes so covered with petechiae as to become of a dark livid hue after death, recalling the name Black Death (Cabiadis).

The occurrence of the above symptoms, especially the first, in an idiopathic fever attacking many persons at one time is sufficient to make the diagnosis of plague.

A very notable and fatal form of the disease is that in which haemorrhages from the lungs, stomach, bowels, nose, &c., occur. These are of the worst omen, and are seen in some cases where there are no buboes, and which are rapidly fatal. This was observed in Irak in recent epidemics, in the outbreak on the Volga in 1878-79, and in the plague of India. It was a noticeable symptom in the black death, and was observed even in the plague of the 6th century. The bleeding is mostly from the lungs, and is sometimes associated with other symptoms of lung affection. This form of the disease appears, however, to have no distinct historical or geographical limit. A similar haemorrhagic form has been observed in small-pox and scarlet fever, and is always extremely fatal.

In all plague epidemics cases occur in which death takes place very rapidly, even within twenty-four hours, without the development of the special symptoms of the disease. Such cases are reported by Diemerbroek, Hodges, and others in the 17th century, and have been observed in recent epidemics in Irak, as well as in the recent plague on the Volga. Some are more like cases of poisoning than of infection, and much resemble the instances of death from the exhalations of dead bodies (cadaveric poisoning) which are met with from time to time. It is these which have given rise to the expression fulminant plague.

Duration.— The duration of an attack of plague may be from some hours to a month. Three-fifths of the cases observed by Mr Colvill were fatal on the third day, and the majority of cases in India had the same termination (Francis). Five-sixths of fatal cases end by the fifth day. Most of those who survive the fifth day get well; after the seventh day a patient in Baghdad was considered by his friends safe; and in Mr Colvill’s cases only 4 per cent, of fatal cases died after the tenth day. In non-fatal cases with suppurating buboes the disease may be protracted to two or three weeks or a month.

Mortality.— Plague is the most fatal of all known diseases which affect large numbers of people. The mortality, according to official registers in Baghdad, was 55 ’ 7 per cent, of those attacked. Dr Cabiadis thinks this too high, owing to many cases of recovery not being reported. But in some epidemics the proportion of fatal cases is much higher. In Vetlanka it was about 90 per cent., and in some other villages on the Volga every person who took the disease died. The older accounts do not give the proportion of deaths and attacks.

Morbid Anatomy.— Examinations after death have not done much to elucidate the nature of plague, except negatively. The appearances are those of death from an acute infective disease, and resemble those of typhus, except for the special affection of the lymphatic glands. The brain and the lungs are found to contain excess of blood; the right side of the heart distended, the blood darkcoloured and undergoing rapid decomposition. The spleen is found enlarged, and in a less degree the liver. The stomach and intestinal canal often show signs of inflammation and haemorrhage, sometimes ulceration. The characteristic swelling of the lymphatic glands, both external and internal, is often accompanied by inflammation of the cellular tissue around. Petechial patches are sometimes found on the internal organs. Pathology of Plague.— All that is known of plague goes to show that it is a specific febrile disease depending on the reception into the body of a specific organic contagion, which becomes multiplied in the body of the patient. Analogy makes it very probable that this contagion is a living organism of the class Bacteria, but the suspected organism has not yet been discovered. The nearest ally of plague is typhus fever, so that some authorities have spoken of it as the typhus of hot climates, modified by temperature, &c., but this opinion does not appear to have ever been held by any competent physician who has examined the disease at first hand. It appears to be as distinct from typhus as this is from enteric fever, or other so-called typhoid diseases. It has also been thought that plague is related to intermittent or remittent malarious fevers; but the most recent observations show that there is no real connexion between these diseases. In India, says Dr Francis, neither intermission nor remission has ever been observed in plague. It is quite distinct from and in no way modified by the types of fever that are caused by malaria. Dr Cabiadis speaks to the same effect of plague in Irak, and insists that the physical conditions which favour the production of marsh poison are not necessarily favourable to plague.

External Conditions of Plague.— The nature of the soil has little influence on plague. It may flourish in alluvial deltas, on calcareous ridges or granitic mountains. Moisture in the soil has generally been thought to be an important factor in its production, but, though often found in marsh situations, such as the banks of the Nile, the Euphrates, or even the Volga, it also occurs in India at elevations approaching 7000 feet, and in Kurdistan at 5000 to 6000 feet above the sea.

The temperature most favourable to plague is a moderately high one. The disease is unknown in the tropics. When prevalent in Egypt it was said never to penetrate farther south than Assouan. It has not crossed the plains of India within historic times. Where the disease does occur, a temperature of 80° to 85° or more, combined with absence of moisture, usually stops the epidemic. In Egypt it was observed to cease as an epidemic almost suddenly about the 2 2d to 24th of June, and not to begin again till September. In Irak it dies out suddenly during the summer. When the temperature rises above 86° it begins to diminish; and it ceases abruptly at a temperature of 113°. In India it has been observed by Dr Francis when the temperature of his tent was 83° to 95°, or in a grass hut to 105°, while the air was moist; but he thinks a lower temperature with dryness renders the poison inert.

On the other hand, in northern countries, the disease is usually checked by the cold of winter, starts up in the spring, and is most active in August and September. To this rule there have been some remarkable exceptions, such as the epidemic on the Volga in 1878-79, which raged during severe winter weather, and the great plague of Moscow in 1770.

Sanitary Conditions.— Of all the co-operating causes of the plague, uncleanliness is the most powerful,—meaning by this the accumulation of decaying animal matter around human bodies or dwellings. The saturation of the soil with filth is perhaps the most important point. A plague seat in Mesopotamia is thus described by Colvill :—“The ground is so saturated with moisture that the refuse of the village is neither absorbed nor evaporated, but . . . acquires the form of a bluish-black oily fluid, which surrounds the huts and covers the paths, and stains the walls 2 feet from the ground; and in fact the village is in such a state of filth that it requires to be seen to be believed.” Of the people among whom the Pali plague of India raged it is said “they were filthy beyond conception” (Francis). There can be little doubt that European cities in the Middle Ages, and down to the 17th century, presented very similar conditions. These conditions may be considered to act by supplying a suitable environment for the life and growth of the organized poison (or bacterium) outside the human body. Where these are wanting one of the main factors in the spread and permanence of the disease will be absent, a fact which makes it probable that increased cleanliness is the chief cause of the disappearance of plague from Europe.

Overcrowded dwellings, especially with deficient ventilation, greatly favour the spread of the disease; but this is not necessarily correlative with density of population, and plague may flourish in thinly peopled countries.

Of social conditions poverty has by far the most powerful influence on the spread and development of plague. Many plague epidemics have followed on years of famine, or been connected with destruction of crops and cattle. The races among which the disease is endemic are almost without exception under-nourished, if not destitute. In the villages on the Volga there appeared to the writer, in 1879, to be little destitution, though the diet of the people was very meagre. In all city epidemics the poor are the chief or almost the only sufferers. This is as true of Baghdad in the 19th century as it was of London in the 17 th. Those of the upper classes who have been attacked have been chiefly doctors, clergy, officials, and others whose occupations take them among the sick.

Origin and Spread of Plague.— Although the above-mentioned conditions are those in which plague originates, and may be considered in a general way essential to its continued existence, it is plain that they do not account for its origin. Poverty, overcrowding, filth, and marsh soil, with a temperature suited to plague, occur in many parts of the world where this disease has never been heard of or has ceased to exist. The geographical distribution of diseases cannot, any more than the distribution of plants or animals, be explained by climatic causes alone. With regard to plague it is quite clear that there are some parts of the world where it is at home, or, as the phrase is, “endemic.” In other parts it is probable (or, as some think, certain) that its existence, and even its periodical recurrence, depend on importation from an endemic centre. Although it is not always easy to distinguish between these cases, they must be considered separately.

In the case of an endemic disease we suppose that the poison is either kept in existence by continued transmission from one case to another, or that it can subsist outside the human body in soil, water, or otherwise. The first mode of existence is that of a pure contagious disease, such as small-pox; and it is plain that this mode of continued existence obtains in the case of plague also. It is not, however, clear that the second may not also be one of the modes of existence of plague, which would then be a so-called “miasmatic” disease like ague, as well as a contagious one. In India, for instance, the disease appears as if it depended on a poison in the soil, since it returns years after to the same spot, appearing in many villages simultaneously; and some morbid influence causes the death of animals (rats) which live under ground. Similar facts have been observed in China; and, if further inquiry should confirm the hypothesis, it would show that plague is (like anthrax or the “steppe murrain” of cattle) both miasmatic and contagious. If so, there is no difficulty in supposing the disease to be carried by contagion to a distant part, and there to be established in the soil, for a longer or shorter period, as the conditions are more or less favourable. The adoption of this hypothesis would remove many of the difficulties attending the explanation of plague epidemics, and to some extent reconcile the controversies of the last three centuries between the il contagionist” and “non-contagionist” schools. It has been maintained by the former that European epidemics have always been caused by the importation of the disease from its home in the East, by the latter that it arose on European soil in the same way as in Egypt or Syria.

In the case of an imported n on-endemic disease, the only question which arises is how the importation is effected,—whether the disease may be brought by the air alone, whether by infected persons only, or whether also by objects which have been in close relation to infected persons. Transmission of the disease by the air cannot be pronounced impossible: and there are facts to show that it is even probable with distances measured by yards, or possibly even hundreds of yards; but there is no evidence whatever that the disease has ever been carried by the air over distances measured by miles. Transmission of the disease by infected persons over longer or shorter distances, and from one country to another, is an established fact. Transmission by infected objects over great distances and from one country to another seems less clearly established. The last two cases must be separately considered.

1. It is clear that the first necessary condition to such transmission is contagion, or transference of the disease from the sick to the healthy. The existence of contagion is shown by such facts as these :—when a case of plague breaks out in a house the other inmates are extremely likely to take the disease; and even in severe forms the plague does not cease till it has affected all or nearly all the household. This is indisputably an almost universal law. In the plague of London in 1603 it was said the disease entered Jιardly any house but it seized all that lived in it. And in 1879, on the Volga, in one village, as was ascertained by Mr Colvill and the present writer, the plague attacked five houses containing thirty-three persons, all of whom except two took the disease and died. In this respect plague resembles typhus. In the next place the disease will spread from an infected house to persons who have close relations with it. Thus in the villages on the Volga it was noticed that after one family was affected cousins and relations by marriage were the next to be attacked. Doctors and those visiting the house are also exposed to the risk, though in a less degree. In Vetlanka on the Volga three physicians and six surgical assistants died. On the other hand, doctors in some instances have singularly escaped from being attacked by the disease. In Egypt, in 1835, out of ten French physicians engaged one only died, nor was this immunity secured by any precautions. These experiences do not prove that the disease is not contagious, but they modify the exaggerated notions which have been held on the subject. The facts appear to be expressed by saying that it may undoubtedly be communicated from one person to another, but chiefly by breathing the air of the sick room, and this generally from prolonged not from momentary exposure,— so that the possibility of communication by chance meetings and similar contingencies may be disregarded. This view is that of Dr Cabiadis and others who have studied plague in Irak where no doctor or assistant, with one exception, suffered from the disease. It is not inconsistent with the experience recorded in Egypt. But it is clear that the intensity of contagion varies greatly in different epidemics. Modern experience contradicts the belief formerly entertained that contact with plague patients was the only or even the chief means of acquiring the disease. Everything tends to show that the atmosphere...