PLAGUE 567 less ossified and divided into separate vertebra, and even when it forms a continuous chorda dorsalis the divisions are indicated by trans- verse partitions ; the skull is united to the spine by a joint with a conical cavity, and the former is a simple cartilaginous capsule, with- out sutures, having a separate cartilaginous arch which performs the office of upper jaw ; the mouth is arched, very wide on the lower surface, and at some distance from the snout, which is much developed for the accommoda- tion of the large nasal capsules ; the teeth are in numerous rows, the inner coming forward to replace those worn away by use ; the bran- chial sacs are separated, with five or more dis- tinct openings on the sides or lower parts of the body ; the gills consist of membranous folds or plane surfaces, without the pectinated arrange- ment of osseous fishes, and with a pseudo- branchia ; there is no swimming bladder ; the scapular arch is detached from the head, and the ventrals are abdominal ; on the upper sur- face of the head, behind the eyes, in most, is a pair of spiracles, communicating with the pharynx ; the skin is covered with hard rough grains or scattered spines ; in the arterial bulb are from two to five transverse rows of semi- lunar valves ; the intestine has a spiral valve ; the optic nerves do not decussate, but are con- nected by a commissure, and there is no arterial plexus between the layers of the choroid coat of the eye. The secreting reproductive organs communicate with the ureters, and end in a rudimentary process in the cloaca ; the claspers are present in the males as appendages to the posterior edge of the anal fins, fissured toward the end, and communicating with a ca3cal sub- cutaneous sac, well lubricated with mucus, and are true intromittent organs ; the ovaries are smaller than in osseous fishes, and the ova very few ; some genera are viviparous, others oviparous, and others ovo-viviparous. PLAGUE (Gr. TrA^, a blow), an aggravated malignant fever, endemic in the East, and fre- quently epidemic. The words pestis and pes- tilentia, the synonymes of plague, as well as the corresponding Greek word used by the old writers, must be taken as meaning nothing more than an epidemic fever. True plague is a contagious fever characterized by an eruption of carbuncles and buboes. Formerly plague occasionally prevailed in many places of north- ern Europe. Before its last visitation in 1665, it invaded England, according to Sydenham, every 30 or 40 years. Marseilles suffered from it in 1720, Moscow in 1771 and 1772, and some points in the Neapolitan dominions as late as 1815 and 1816. The celebrated "black death," which ravaged all Europe in the middle of the 14th century, appears to have been the oriental plague. As in all severe epidemics of the dis- ease, at its commencement many of the patients died before the development of the peculiar eruption; but the general occurrence of car- buncles and buboes is sufficiently authentica- ted. It derived its name from the gangrenous eschars formed by the carbuncles, or perhaps from the petechiaB which accompanied the disease. A report made to the French acad- emy (Rapport d Vacademie royale de medecine sur la peate et les quarantaines, &c., Paris, 1846) says : "1. At present the countries where the plague still originates are in the first place Egypt, afterward Syria and the two Turkeys. It is probable, however, that the plague may be developed without importation in the regencies of Tripoli and Tunis, and in the empire of Morocco. 2. In those countries the conditions which determine and favor its development are the habitation of alluvial or marshy grounds; a hot, moist atmosphere; low, badly aired, and crowded houses ; the accumu- lation of a great quantity of animal and vege- table matters in a state of putrefaction; a scanty and unwholesome diet ; great moral and physical destitution ; the negligence of the laws of public and private hygiene. 3. Sporadic plague does not seem to be transmissible. Epi- demic plague is transmissible both in the local- ities where the plague is raging and without them. 4, It is transmitted by means of mias- mata given out by the bodies of the sick ; these miasmata, in close and ill ventilated places, may create centres of pestilential infection. It results from the observations made at the lazarettos for more than a year that merchan- dise does not transmit the plague." The period of incubation in plague seems in no case to be beyond eight days. The course of the disease varies very much in different cases. Some- times the local symptoms first show them- selves, and the fever which follows is com- paratively mild; at other times the patient is rapidly overwhelmed by the violence of the constitutional disorder, and dies without the appearance of carbuncles or buboes ; between these extremes, and tending to one form or the other, the disease presents every variety. In its milder forms small spots like flea bites first make their appearance, especially on the parts of the body exposed to the air ; these enlarge, become dusky, and are covered by vesicles or phlyctense filled with a dark-colored fluid. The base of the spots is hard; it becomes black, forming a gangrenous eschar with a circumfer- ence of an inch or an inch and a half in diame- ter ; these are the carbuncles. This process is attended with more or less fever, which as the eschar becomes detached gradually subsides. Often consequent upon the appearance of the carbuncles, glandular swellings form, com- monly in the groins or armpits, more rarely in the neck. These buboes, as they are termed, occasionally disappear without suppuration; more generally after a time pus is formed, some- times healthy, sometimes thin and sanious. Cases in which buboes appear are attended with a higher grade of fever and with pro- founder depression of the vital forces ; head- ache, restlessness, chills, and vertigo are Qom- monly present ; the eyes are red and muddy, the tongue coated, the skin hot and dry ; the
