Paralysis of different sets of muscles, of different members, or of the entire body may occur. Frequently, varying degrees of aphasia are noted. This symptom may be due to central disturbances, or to local interference of a cervical bubo, or the ædema with the vocal apparatus.

Blood.-A drop of blood from puncture of the ear seems more watery and of a lighter color than normal. If drawn when the circulation is beginning to fail, it may be more or less venous in appearance. No change is noted in the red blood cells. Leucocytosis of the polymorphonuclear type is usually present from the beginning of the disease, varying from eight to forty-five thousand, or even higher, according to some observers. The blood platelets are usually increased in number.

Early in plague the blood is practically free from organisms. Gradually the organisms gain access to and rapidly multiply in it as the disease progresses. The bacilli enter blood either through the lymphatic vessels or by direct growth through the walls of the veins in the neighborhood of the bubo or buboes. During the later stages of plague and at autopsy the bacilli are practically always present. In cases upon which systematic blood examinations have been made, bacilli have been found from twenty-four to forty-eight hours before death. When organisms first appear in the blood, only a few may be seen on each slide. Often only one is found. The number rapidly increases, and frequently the blood is, just before death, practically a pure culture of the plague bacillus. The bacilli occur in the blood singly, in pairs, in chains of from four to five, and in clumps. Then capsules and characteristic staining are easily demonstrated. Appearance of the bacilli in the blood naturally gives an

unfavorable prognosis.

From what has been said it is evident that examination of the blood is of very little diagnostic value during early stages of the disease, but later is of the utmost importance. During an epidemic the leucocytosis and increased number of blood platelets are important points in the diagnosis, even in the absence of bacilli, especially in differentiating from malaria and typhoid fever.

Fever.-Plague does not present a characteristic fever curve. The fever may be a simple continuous fever, or may remit, and even intermit. Morning depression and evening elevation are usual. The variation is usually from one to two degrees. Occasionally fever is noted for twenty-four to forty-eight hours after the onset of the disease, followed by normal temperature for twenty-four to forty-eight hours, and then sudden rise in temperature with severe symptoms and death. In one case of this kind observed the patient died within ten hours after the second onset of fever. Frequently the temperature is seen to drop below normal, to be followed within a few hours with a sudden rise and death. Temperature in plague cases usually varies between 102° and 104° Fahrenheit; occasionally 107° has been noted. Height of fever does not seem to bear any relation to the severity of the attack or to the accompanying delirium. Temperature rarely terminates by crisis, but usually gradually subsides to or below normal. A subnormal temperature during the convalescent stage is very common. Fever continues from six to ten days. In the event of the suppuration of the glands the fever shows the ordinary septic type. This type of fever may develop during the later stages of the disease, or some days after the true plague temperature has become normal. On opening the bubo the temperature usually rapidly falls. The degree of fever in plague is easily reduced by the cold bath, but is little affected by the ordinary antipyretic drugs.

Special senses.-During the height of a plague attack deafness may develop, especially in hemorrhagic cases, and in those with cervical primary buboes of the first order. Prognosis is usually favorable.

The conjunctivæ are more or less injected, and true conjunctivitis may superinvene. Keratitis, iritis, and panophthalmitis may occur.

Epidemiology-Portal of entry.-Experience has shown that plague is usually, if not always, an infectious disease, and that the organism must actually be introduced into the system before infection can take place. It is difficult, and usually impossible, to tell in a given case the portal of entry.

There is usually no local reaction about small scratches, etc., which are frequently seen on the extremities when a femoral, inguinal, or axillary bubo is present. Circumstantial evidence goes to show that the organisms gain access to the system through an abrasion of the skin. This abrasion may be either gross or microscopic. From the tissues about the abrasion the bacilli are taken up by the lymph and carried to the lymphatic glands.

The organisms may enter through the external mucous membrane, especially in children. Infection may also occur through the alimentary tract, especially when cold food is used. Inhalation of infected dust in factories or of dried sputum from pneumonic cases is another method of infection, the bacilli entering through the air passages or lungs. It is quite possible to contract the disease through sexual interIn one of my cases this seemed to be the most probable avenue of infection.

course.

Incubation period.-From time to time many experiments have been accidentally performed, which served in a way to determine the period of incubation. From these experiments, and from the large number of people kept in isolation camps it has been found that from two to ten days is the ordinary limit of the period of incubation, usually from three to six or seven days. During the epidemic in India in 1896 and 1897 no case came under observation with an incubation period longer than ten days. Some authors, however, claim that it may be as long as fifteen days. Direct transmission.-Excretions from the patient, hemorrhages from the nose and lungs, menstrual flow, vomitus, fæces, secretions from pustules and carbuncles, and pus from the bubo contain the bacilli in varying numbers. Any or all may serve as the medium of direct infection. The bacilli have not been demonstrated in the perspiration. In air the plague organism has a very short life; when exposed to direct sunlight it is killed within three hours. An infection may occur while handling any of the above-mentioned excretions, or the bed clothing, etc., used by a patient. The sputum is of especial importance, as the patient may, with this secretion, infect a very large area; this is especially true in plague pneumonia. Naturally the cadaver is infected.

Indirect transmissions.-The plague organism, even when dry, has an indefinite life under certain conditions. Nonexposure to light does much to lengthen this period. Clothing, exposed fabrics, or dust or merchandise infected by means of dead rats or by handling in places where plague existed, or in whatever way infected, may transmit the disease. In this laboratory the plague organism was recovered from dry paper kept in a thermostat for forty-five days. How much longer it would live has not yet been determined. The organism of plague has not yet been found in the esteros or sewers of Manila, but there is no reason to doubt that it might live for considerable time in these locations. Kitasato has found the bacilli in fabrics brought from Bombay. Infected rooms, not properly disinfected, may serve to transmit the disease. Cadavers, even when buried, harbor the organism. Experiments are now being carried on to show how long the bacillus lives when so buried. Thus far, it has been recovered after two months. It has not yet been determined whether the infection is carried in water. Numerous cases are on record where infection has been carried by clothing, etc., which had been packed away for months.

Spreading of the disease is favored by unhygienic conditions, and crowding of dwellings. Individual habits also play an important part. In practically all epidemics, in whatever part of the world, the larger proportion of cases has occurred in sections of the towns having the smallest and poorest ventilated houses, with defective drainage and water supply. In these particular districts people usually crowd together and live under the filthiest conditions. In the better portion of a city infected with plague but few, if any, cases occur.

Spreading of the disease.-Plague infection may be carried from place to place in various ways. Among others, the removal of a person sick with the disease is an important means, as is also the arrival from an infected place of a person who has been exposed to contagion and for whom the incubation period has not elapsed. Under these circumstances the organisms are spread about in the fæces, urine, sputum, and to some extent in the bed clothing of the sick person; the well, of course, not carrying the infection except by clothing, etc., until attacked by plague. The nature of the disease and the precautions to be taken against it are unknown to the general public, therefore its further spread may be easily accounted for. It has been noted that ordinarily first cases imported into a new field attract little attention, as but few cases immediately follow the infection. Bacilli have been found in fabrics brought in bulk from infected ports. This is a most dangerous method of spreading the disease, as these fabrics enter a new field and are handled by the inhabitants, who are thus brought into direct contact with the organisms. The disease may in this way be spread over a large area before its true nature is discovered. The emigration of rats from district to district is also an important factor in the spreading of the plague. Infected rats from ships may also carry the disease from one country to another.

Extension of the epidemic.-When introduced into a new district, plague does not make rapid progress at first. Usually considerable time elapses between each case, and the disease may linger practically without manifestation for one, or, possibly, for two or more years. During this time, however, different areas are becoming infected. These later serve as starting points for a more or less extensive epidemic. Even with beginning epidemic prevalence, the disease spreads slowly, not going from house to house and from district to district, but jumping from one house to a distant one, in the same or neighboring blocks, or in an entirely different part of the city. This is undoubtedly accounted for by the visiting of people in the infected house, or by the using of commodities bought from an infected store. As time goes

on, the number of infected places naturally increases, and with this increase an increased number of cases of the disease may be looked for. In an infected city these infected areas may be considered to be the endemic location of the disease for that particular city.

The yearly duration of an epidemic of plague is usually but a few months; rarely does it last longer than six. The majority of the cases occur within two or three months. As a rule, an epidemic of plague has a rather sudden decrease toward the latter part of its course. A few mild cases are noted, however, from time to time for some months after the epidemic has subsided. When once introduced, plague continues from year to year, with an occasional intermission of a year, for an indefinite time. The disease is kept alive during the intervals between the epidemics by mild cases, infected fabrics, houses, etc.

Duration of the disease.-According to most observers, the larger proportion of deaths occurs within the first eight days, usually from the third to the fifth. In severe forms of pest, death may occur within twenty-fours after onset of the first symptoms. When death occurs late during the second week of the disease, secondary infections are usually present. The average duration of symptoms of plague proper is from six to eight days. Secondary infections may prolong the attack from four to six weeks. The convalescent period may be short or long drawn out, due to the severe prostration caused by the attack. Emaciation accompanying a short attack may not be noticeable, but is usually well marked in severe attacks of long standing. General extensive necrosis of all of the organs predisposes the convalescent to secondary infections: suppuration of buboes, parotitis, skin abscesses, suppuration of the middle ear, etc. During the convalescent period, recrudescence of the disease may occur from the first to the eighth week. The prognosis is unfavorable. The same individual may be subjected to two or more attacks of plague, occurring at shorter or longer intervals. Therefore attacks confer only a relative immunity.

Plague among animals.-Plague has been found in practically all the domestic animals. From earliest times writers have noted the susceptibility of rats and mice during plague epidemics. In I Samuel v and vi, plague is mentioned as existing among the Philistines, and the pollution of the fields by mice is noted. To counteract this pollution the Philistines made gold images of mice to appease the gods. Avicena, in 1000 A. D., says that when rats are affected with plague they come out of their holes and act as if drunken. Nicepheros Gregaros, in 1348 A. D., says that rats are affected by plague, and come out of the walls of the houses, etc. He also mentions that dogs and horses are affected. In recent years rats have undoubtedly played an important rôle in the propagation of plague. In numerous instances, before the existence of plague became generally known, large numbers of dead rats have been found in streets, alleyways, etc. Usually during a severe epidemic among the rats they emigrate, evidently to escape the sickness. In this way they carry the disease from district to district. Epidemics are not always noted among rats, even when many people are affected with plague. There is no doubt as to the nature of the disease in the rat, as numerous observers have made careful studies and autopsies and have invariably found evidences of true plague. The source of plague in this animal has not yet been definitely determined and, indeed, is a difficult question to settle. As the plague organism is probably long lived, rats may acquire the disease from some old fabric which was formerly infected with plague, pick up the organism in the ground, or receive the infection from a patient sick of plague. In these instances what might otherwise be a harmless organism may, on new soil, become virulent. From time immemorial, insects, fleas, mosquitoes, etc., have been believed to play an active part in spreading plague, and only recently has the opinion been advanced that fleas are the active agents in spreading the disease from rat to rat, and from rat to man.

Climatology. The history of epidemics of plague shows that the disease may flourish in the tropic, temperate and frigid zones, at the sea level, and at high elevations, and during all seasons. When once introduced into a locality, plague seems to favor certain seasons of the year, and the yearly epidemics follow these seasons with great regularity. In the Tropics the ending of the cold season and the beginning of the hot, dry season is the favored time. It has been noted that when the temperature reaches its highest point plague begins to decrease. At the end of the dry season and the beginning of the rainy season the epidemic is practically ended. A few cases appear from time to time during the entire rainy season.

Age, sex, race, and occupation.-Age seems to have but little importance as to susceptibility to the disease. Children and old people are alike affected. The great majority of cases, however, range between 20 and 40 years. After 50 years the number of cases is proportionately small. The disease is about equally distributed between the two sexes. All races are alike prone to infection. The few cases occur

ring among Europeans is due more to social conditions than to racial immunity. Laborers at all trades are affected, but it has been noted that those continually working in water and oil rarely contract the disease.

Plague may be associated with any of the ordinary diseases, and its severest type often accompanies diseases of a chronic nature.

Mortality.-Mortality in the several epidemics of plague varies greatly, ranging from 30 per cent to 93 per cent. In Manila, in 1900, the mortality was 73 per cent, including all cases.

Methods to be used when the presence of the plague is suspected.-An early diagnosis of first cases is essential. This may be made by a thorough microscopical and bacteriological examination, or, in the event of death, by autopsy. The agglutination test is of diagnostic value; it is usually positive after the ninth or tenth day.

Suspected cases should be isolated and closely observed. Those associated with the suspected cases should also be isolated in a detention camp for at least ten days. The effects and dwelling of the suspected case should be thoroughly disinfected. Unhygienic localities should be cleaned and disinfected. It would be cheaper to destroy these sections than to endure from year to year expensive methods of handling the disease and the check to commerce usually experienced.

The plague hospital or detention camp should be in an isolated spot and so constructed that all of the infectious material may be easily sterilized.

Methods pursued in combating an epidemic.-The ordinary methods pursued are: Searching for and removal of sick; isolation of those known to have been exposed to the disease; cleaning and disinfection of houses in which sick have been found, including its surroundings, furniture, clothing, etc., used by the occupants.

Early removal of sick reduces to a minimum the amount of infectious material which they may scatter in their immediate vicinity. Information regarding sick is obtained either by house-to-house inspection or by dividing the city into districts in which the inhabitants are required to report all cases of sickness to the nearest health officer, whose duty it is to diagnose and dispose of each case. Positive and suspected cases of plague should be transferred to the hospital. Those exposed to contagion should be isolated, preferably near the plague hospital. Ten days is the usual period of isolation.

The house and surroundings should be thoroughly cleaned and disinfected. For this purpose, carbolic acid, bichloride of mercury, tricesol, or any other cheap, reliable disinfectant may be used. The furniture should be washed with disinfectants, and the clothing, etc., especially that used by the sick, should be disinfected by steam or soaked in a 3 to 5 per cent solution of carbolic, or a 1 to 1,000 bichloride solution, for one hour.

The general hygiene of the infected cleaning of houses, yards, streets, and exterminate the rats should be made. of their hiding places, etc.

locality should be improved. A systematic sewers should be carried out. An attempt to This may be done by poison, depriving them

The inhabitants of infected localities should be taught the nature of plague, and the individual precautions to be taken against it. This may be done through the newspapers, posters in each dialect and language, schools, churches, etc.

Individual prophylaxis.-Those coming in direct contact with the disease should disinfect the hands with carbolic acid or bichloride of mercury immediately after exposure. When cuts, scratches, etc., are on exposed parts, infectious material should not be handled. General cleanliness should be maintained. The clothing should be covered; the feet protected; recently cooked food, only, used, and infected localities, houses, stores, etc., as far as possible, avoided.

Quarantine regulations can not be too rigorously enforced.

No passengers nor animals should be allowed to leave the infected port except in the case of passengers after a period of detention of ten days; all baggage and cargo should be thoroughly disinfected. If during an ocean voyage of more than ten days' duration plague does not develop aboard ship, the passengers may be allowed to land; otherwise, a quarantine should be established, and the effects of the passengers, cargo, and ship should be disinfected.

General clinical observations.-Writers on plague have given many distinct forms to the disease, but the following completely cover the ground: Pestis minor, pestis bubonica, septicemic plague, pneumonic plague. Of these, the bubonic type is most common, the septicemic form second in frequency, and pestis minor predominant before and after an epidemic.

Pestis minor is often noted many months before and after the real epidemic of plague. It may appear in sporadic cases or in a light epidemical form. Usually, when isolated, one or more buboes develop, with more or less fever. The symptoms are, as a rule, light. The organisms may be found in the bubo and the blood, but,

as a rule, are not highly pathogenic. The bubo may go on to suppuration or resolution. Afterwards, severe epidemic cases are seen, in which a single gland or group of glands is enlarged, painful, associated with more or less debility, dizziness, headache, sleeplessness, some disturbance of digestion, and more or less fever. The nature of these cases is, in part, determined by the place of dwelling. They most frequently develop in houses in which plague was common during an epidemic.

The bubonic type.-Ordinarily, onset of the disease is sudden, without any prodromal symptoms whatever. Occasionally a train of prodromal symptoms may be noted for twenty-four to thirty-six hours before the onset of fever. These symptoms are usually a general bad feeling, weakness, light chills, pains in the legs, some headache, sleeplessness, and loss of appetite. There may be some vomiting and dull pain about the seat of the future bubo. Usually, as stated, the disease begins suddenly with a fever. The fever may rise suddenly, reaching its highest point during the first day of the disease, or it may gradually rise, taking from two to three days to reach the fastigium. The onset of the fever may be accompanied with an initial chill of varying intensity. In addition to the initial chills, chills of more or less severity may continue at irregular intervals throughout the course of the disease. These chills do not seem to bear any direct relationship to the course of the fever or to the severity of the attack. The bubo usually develops from the second to the fourth day of the disease. Patients are usually admitted to the hospital during the bubonic stage. The following general conditions have been noted: Perspiration apparently greatly diminished, or entirely absent; occasionally more or less profuse periodical perspirations; skin usually cedematous, especially on the extremities; frequently intense itching; some pain in skin from time to time; over the bubo more or less reddening; skin usually dry and hot.

In the early epidemics of plague, subcutaneous hemorrhages were evidently more frequent than in recent ones. Ordinarily, hemorrhages do not appear until late in the course of the disease, or just before death.

The facial expression is often most peculiar, and, when once seen, can never be forgotten. It seems to be a mixture of pain, fear, and anxiety. The eyes may or may not be deeply sunken, and dull in appearance. The pupils are usually slightly dilated; in some cases the eyes have a fixed, staring appearance. Convergent strabismus is frequent.

The tongue is usually heavily coated white, and later during the disease is of a brownish color along the center. The papillæ usually stand out prominently and the edges are bright red and oedematous. The entire tongue seems to be swollen. The pharynx is usually reddened and may be deeply congested. The tonsils do not show any constant symptoms. The veins of the neck are usually distended and pulsating.

The movements of the two sides of the thorax are equal. Palpation usually shows the vocal fremitus increased. The percussion note may be somewhat defective, and ausculation usually reveals a slightly roughened breathing sound, with more or less moist rales. Respiration is usually somewhat shallow, apparently labored, and increased in frequency, often reaching a rate as high as fifty or sixty per minute. This is undoubtedly due to the extreme congestion, edema, and bronchitis or bronchopneumonia noted in the lungs. The heart is usually somewhat dilated, the area of pulsation increased and a soft systolic murmur audible. The pulse is weak, often dicrotic, small, and easily compressed. The rate is usually increased, ranging from 90 to 140, or even as high as 180, beats per minute.

The abdomen usually presents nothing of interest. Seldom is the spleen palpable and the liver is usually normal in size. When the mesenteric glands are markedly involved, considerable pain may be felt over the entire abdomen. Occasionally the involved iliac glands may cause considerable pain.

The urine presents the usual febrile characteristics, diminished quantity, with some blood and pus cells. Occasionally there may be a complete anuria. There may be either diarrhea or constipation.

As has been noted, the primary bubo of the first order may be preceded by indefinite pain in advance of the usual initial symptoms of the disease. Beginning with the initial symptoms, the glands may begin to enlarge and be very painful. Ordinarily, however, the glands do not begin to enlarge until from the second to the fourth day of the disease. The rapidity of the processes at work in the glands varies greatly. Within a few hours the gland may reach its largest size; ordinarily, however, the process requires from two to four days. During the stage of development of the bubo the pain is usually severe. In comatose cases, pressure on the bubo may elicit evidences of tenderness when other attempts fail to arouse the patient. When the bubo is fully developed, the pain usually diminishes in intensity or entirely disappears. In the event of suppuration more or less pain may be present. In

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