Imágenes de páginas
PDF
EPUB

Circulation.

marked in the smaller vessels. The rate of movement of the blood through the arteries in man can only be roughly calculated from experiments on animals. Volkmann finds that in the carotids of mammals, the average velocity of the blood-stream is about 12 in. per second; he has likewise ascertained that the velocity is greater in arteries lying near than in those at a distance from the heart, that it is not increased by an augmentation in the number of pulsations, but that it is greatly augmented by an increase in the volume of the blood, and lessened by its diminution.

3. It has long been a debated point, whether the capillary C. is influenced by any other agency than the contractility of the heart and arteries. Harvey believed that the action of the heart alone was sufficient to send the blood through the whole circuit, and in recent times his view has been supported by J. Müller and other eminent physiologists. On the other hand, prof. Draper of New York holds the opposite extreme view, asserting that “it is now on all hands conceded that the heart discharges a very subsi. diary duty." We believe that Bichat was the first to maintain the opinion, that the capillaries are organs of propulsion, and are alone concerned in returning the blood to the heart through the veins. Although Bichat attributed too great power to the capilJaries, there cannot be a doubt that the movement of the blood through these vessels is not solely due to the heart; in short, that there is what may be termed a capillary power. The following are a few of the facts proving this to be the case: 1. On watching the C. in the web of a frog's foot, it is at first seen to go on with perfect regularity. After a time, however, various changes are observed, which cannot be attributed to the heart, such as alterations in the size of some capillaries, and in the velocities of the currents passing through them, and occasionally even a reversal in the direction of some of the lesser currents. 2. In cold blooded animals, the movement of the blood in the capillaries continues long after the excision of the heart. 3. Actual processes of secretion not unfrequently continue after death; sweat, for instance, may be exuded from the skin; and other secretions may be formed by their respective glands, which could not take place if the capillary C. had stopped. 4. Cases occasionally occur in which a fetus without a heart is produced, and yet in these cases most of the organs are well developed.

What the nature of this capillary power is, is not clearly known. Prof. Draper and others have endeavored to explain it on the principles of capillary attraction. There is no satisfactory evidence that the capillaries possess true contractility, for, although their diameter is subject to great variations, this may be due simply to the elasticity of their walls. If we could only establish their contractility, the difficulty would be removed.

The rate of movement of the blood through the capillaries is about 1.2 in. per minute in the systemic capillaries of the frog. In the warm-blooded animals it is probably more rapid. From Volkmann's observations, the rate in the dog is about 1.8 in. per minute.

4. It is usually estimated that the venous system contains from two to three times as much blood as the arterial. The latter is probably the more correct ratio, and as the rapidity of blood in the two systems seems to bear an inverse ratio to their respective capacities, the venous blood will move with only one third of the velocity of arterial blood. We have already noticed the occurrence of valves in the venous circulation. Their object is evidently to prevent the reflux of blood; hence they are of important use in the maintenance of this part of the circulation. They are most abun. dant where there is much muscular movement. The movement of blood through the veins is undoubtedly mainly due to the ris a tergo resulting from the contraction of the heart and arteries. This is much assisted in many parts of the system by the constantly recurring pressure of the adjacent muscles upon their trunks. The movement of inspi. ration, by causing a comparative vacuum in the chest, has been supposed by some physi. ologists to assist the flow of venous blood to the heart, and a similar influence has been ascribed to an assumed suction-power of the heart. The contractility of the veins in man is too slight to produce any marked effect on the propulsion of the current. From the investigations of prof. Wharton Jones on the rhythmical contractility of the veins of the bat's wing," we may infer that, in many of the lower animals, it is probably a more efficient power. In connection with this article, consult ARTERY, CAPILLARIES, Pulse, and VEIN.

CIRCULATION OF SAP in plants—its ascent from the root to the leaves and bark, and its partial descent after the elaboration which it undergoes in these organs. The sap. drawn from the ground by the roots (sec OSMOSE) ascends in exogenous plants, which have hitherto been principally the subjects of examination, through the more recent parts of the woody tissue, and especially through the alburnum. The descent of the sap takes place chiefly through the liber or inner bark. It appears certain also that, on its return to the root, only a small portion is excreted, and that the greater part ascends again, readapted to the use of the plant by the excretion which has taken place. Much of the sap which is taken up by the roots is, however, thrown off in perspira. tion by the bark and leaves. The sap is also latterly diffused through the cellular tissue of plants, and very interesting observations have been made by Schultz and others on peculiar movements of the elaborated or descending sap (later). Many physiologists dislike the term circulation applied to sap, as suggesting a closer analogy than really exists to the circulation of the blood in animals. See PLANT, LEAVES, and SAP.

CIRCUMCELLIONES, fanatical Donatists of the 4th c., who got their name from their habits of wandering. They rambled over the country, plundering, burning houses, and murdering those who made resistance, saying that by such means they sought the crown of martyrdom. They styled themselves " Milites Christi Agnostici," and called their chiefs the leaders of the sons of the Holy One. Constantine treated them with forbearance, but under his successor they were put under restriction by the civil power.

CIRCUMCISION (Lat. a cutting around), the cutting off the foreskin (præputium), a rite widely diffused among ancient and modern nations. The prevalent idea among Christians was (and perhaps still.is), that the rite originated with Abraham, who (as we read in Gen. xvii. 9-14) was commanded by God to circumcise himself and his whole household, and to transmit the custom to his descendants. But, as Jahn (Biblische Archäologie, Vienna, 1797-1800) acutely observes, this is inconsistent with the very terms in which the command is expressed, these terms presupposing a knowledge of the rite on the part of Abraham. That it existed previously to the time of the patriarch, how. ever, seems to be indisputable. The researches of modern scholars prove that the Egyptians, for instance, were in the habit of circumcisiug long before Abraham was born. Rawlinson, in a note to his version of Herodotus, remarks that “circumcision was already common in Egypt at least as early as the fourth dynasty of kings, and probably earlier, long before the birth of Abraham, or 1996 B.C.” The testimony borne by the monuments of Upper and Lower Egypt (consult sir Gardiner Wilkinson's Man. ners and Customs of the Ancient Egyptians) is to the same effect, and apparently conclusive. Another argument which has been adduced against its Abrahamic origin, is the fact of its being so extensively practiced. At the present day, it may be traced almost in an unbroken line from China to the cape of Good Hope. It is also a usage in many of the South Sea islands, and the followers of Columbus were much astonished to find it existing in the West Indies, and in Mexico. Recently, too, it has been ascertained to have been long practiced by several tribes in South America. Such being the case, many scholars hold it impossible to suppose that the origin of so universal a rite can be traced to a single Semitic nation, more especially when that nation was peculiarly averse to intercourse with other nations, and in other respects exercised no overt influence on their customs. Whether, as Jahn supposes, Abraham obtained his knowledge of C. from the Egyptians, we cannot determine. It would appear, however, that the Canaanites, among whom he came to reside, were not circumcised, for we read of the prince of Shechem and his people undergoing the operation, that the former might obtain the hand of Dinah, daughter of Jacob; and the institution of it in the family of Abraham was probably sufficient to mark off that family from the surrounding tribes. In the case of Abraham and his descendants, the rite acquired a religious signiticance. It was ordained to be the token or seal of the everlasting covenant between God and his people. Such is the view of St. Paul, who looked upon the C. of the foreskin as symbolical of the C. of the heart; and that along with all that was merely Judaistic and material, it was abrogated by the more spiritual teaching of Christ.

The time for C. among the Jews is the 8th day after the birth of the child; among the Arabians, the 13th year, in remembrance, it is said, of their ancestor Ishmael; among the Kaflirs, at a still later period, marking, in fact, the transition from youth to manhood; and, indeed, each pation seems to have selected the time most agreeable to its own notions of what is prudent or becoming The Abyssinians are the only people professing Christianity among whom C. is practiced. The C. of females, or what is equivalent to such, is not unknown among various African nations. For fuller information in regard to C., consult Sonnini's Travels in Egypt, sir John Marsham’s Chronicus Canon Ægyptiacus, and Winer's Biblisches Realwörterbuch.

CIRCUM FERENCE, or PERIPH'ERY, the curve which incloses a plane figure: thus, we speak of the circumference of a circle, or of an ellipse; but in figures bounded by straight lines, as the triangle, square, and polygon, the term perimeter is employed to designate the whole bounding lines taken together.

CIRCUMNAVIGATION, the term usually applied to the act of sailing round the world, its literal meaning being simply a sailing round. The C. of the globe was at one time considered a great feat, but it is now regarded as one of the most commonplace affairs in a sailor's experience. The first to circumnavigate the globe was Magallaens (q.v.), or Magellan, in Portuguese, in 1519; eighteen years afterwards it was accomplished by a Spaniard; and in 1577 by the illustrious Englishman, Drake. The most celebrated of circumnavigators, however, was capt. James Cook, who, between 1768 and 1779, made three voyages round the world.

CIRCUMPO'LAR STARS, those stars which, in the apparent daily revolution of the sky, do not pass below the horizon of the observer, or, in familiar language, do not set. It will be remembered that the apparent daily motion of the stars is the reflex of the actual rotation of the earth upon an axis which passes through the center of the earth and a point in the sky, near the north, or polar star; that the lines in which the stars scem to move, called lines of daily motion, are the circumferences of circles that are perpendicular to this axis. Hence, if an observer is at the equator, the axis lies in

Circus.

the observer's horizon, the circles of daily motion are all perpendicular to the horizon, and all stars seem to rise and set. If the observer is at a distance from the equator, for example 10° n., the northern end of the celestial axis is raised 10° above the horizon, and any star which is within 10° of the n. pole of the sky will not pass below the horizon in its apparent motion about the pole. The largest circle of the sky which may be drawn about the pole without passing below the horizon, is called the circle of perpetual apparition. A similar circle drawn about the s. pole, without coming above the horizon, is called the circle of perpetual occultation, and the stars within that circle are never visible to the observer in consideration. But, to an observer in the southern hemisphere, having a s. latitude equal to the n. latitude of the first supposed observer, the terms will be transposed; the circle about the s. pole is to him a circle of perpetual apparition, and the stars within it, circumpolar stars; the corresponding circle about the n. pole is the circle of perpetual occultation, the stars within which never appear above his horizon. The radii of the circles of perpetual apparition and occultation are equal, and equal to the latitude of the observer, and to the altitude of the nearest pole. In the northern states the most conspicuous circumpolar constellations are the great and little bear--the latter contain: ing the pole star-and Cassiopeia. In the southern sky the most brilliant constellation is the southern cross.

CIRCUMSTANTIAL EVIDENCE. See EVIDENCE.

CIRCUMVALLATION, in fortification, is a series of works surrounding a place when under siege; not to serve offensively agaivst the place, but to defend the siege-army from an attack from without. It usually consists of a chain of redoubts, either isolated or connected by a line of parapet. Such lines were much used in the sicges of the ancient and middle ages; but in modern times they are not so necessary, because the use of artillery lessens the duration of a siege, and also because the besiegers have generally a corps of observation in the open field, ready to repel any force of the enemy about to succor the besieged. A remarkable example of C. was that at Sebastopol, where, while a circuit of batteries fired upon the town, an outer circuit of redoubts and lines kept off the Russians who were in the open field; but the necessity for this arose out of the smallness of the besieging force compared with that of the besieged. The narrow escape of the allies from utter overthrow at Inkermann, showed the necessity for this external defense. For the relation which C. bears to COUNTERVALLATION, see that article.

CIRCUMVENTION. See FRAUD.
CIRCUS. See HARRIER.

CIRCUS, Tue, of ancient Rome, was a large oblong building adapted for chariot. races and horse-races, and used also for the exhibition of athletic exercises, mock-con. tests, and conflicts of wild beasts. The circensian games were alleged by tradition to have originated in the time of Romulus, when they were dedicated to Consus or Neptune, and called Consualia. After the first war undertaken by Tarquinius Priscus, in which he captured the Latin city of Apiolæ, his victory was celebrated by games. A space was marked out for a C., and the senators and knights were allowed to erect scaffoldings round it for themselves. The games continued to be held annually, and a permanent edifice was soon afterwards constructed. This was distinguished, subsequent to the erection of the Flaminian and other large circi, as the circus maximus. It must have been altered and enlarged at various times. According to different computations, it was capable of holding 150,000, 260,000, or 385,000 persons. Its extent also has been variously estimated. In the time of Julius Cæsar, it was three stadia, or 1875 ft. long, and one stadium, or 625 ft. wide, while the depth of the buildings surrounding the open space was half a stadium, or about 312 feet. All the circi in Rome, of which there were a considerable number, are now completely destroyed; but a small c. on the Appian way, about 2 m. from Rome, known as the circus of Caracalla, is still in a state of preservation. Its construction is believed to have differed very little from that of similar buildings.

Along the sides and at the curved end were ascending ranges of stone seats for the spectators. At the other end, were the carceres, or stalls, which were covered, and furnished with gates, and in which the horses and chariots remained until, on a given signal, the gates were simultaneously flung open. In the center is the spina, a long and broad wall round which the charioteers drove, terminating at both ends at the metæ, or goals-three cones of carved wood which marked the turnings of the course. At each extremity of the carceres is a stone tower. From its gates and castellated appearance, the whole of this side received the name of oppidum, a town. Over the carceres were seats for the president of the games, the consuls, or other distinguished persons. There were four entrances, of which the most important were the porta pompæ, and the porta triumphalis. The games were inaugurated by a procession from the capitol, in which those bearing the images of the gods went first, and were followed by the performers in the games, the consuls, and others. This procession entered through the porta pompa, while the porta triumphalis was that by which the victors left the circus.

The spina, an object conspicuous from its situation, was in general highly decorated by such objects as statues, small temples, aitars, etc. In the spina of the Circus Maxi. mus, two very large obelisks were erected by Augustus and Constantius. This C. was

Cissampelos.

also distinguished by six towers, and by a canal or euripus, formed by Julius Cæsar, to protect the spectators more effectually during the conflicts of wild beasts.

The C. was especially adapted for races, an amusement of which the Romans were passionately fond." The length of a race was seven circuits round the spina, and 25 races were ruu in each day. The number of chariots was usually four. The charioteers adopted different colors, representing the four seasons. Bets and party-spirit ran high, and the victor received a substantial pecuniary reward at the end of the race. The athletic exercises, such as boxing and wrestling, which sometimes terminated fatally, were probably exhibited in the large open space between the carceres and the spina. The ludus Troją was a inock-conflict between young men on horseback. A regular battle was sometimes represented (pugna equestris et pedestris). By the formation of canals and the introduction of vessels, a naumachia, or sea-tight, was occasionally exhibited; but, under the empire, this species of exhibition, as well as the cenatio, was gradually transferred to the amphitheater (q.v.). In providing for the venatio, or hunting of wild beasts, vast sums of money were expended. Animals were procured from every available part of the Roman empire, including Africa and Asia. The exhibition not only afforded an opportunity for the display of private munificence or ostentation, but attained the importance of a political engine, which none who aspired to popularity ventured to overlook. When Pompey opened his new theater, he is said to have given public exhibitions in the C. for five days, during which 500 lions and 20 elephants were destroyed.

In modern times, the C. stands but as the shadow of a name. It is about the same size as the modern theater, and is employed principally for the exhibition of feats of horsemanship and for acrobatic displays.

CIÄRENCES'TER, or CICESTER, a parliamentary borough in Gloucestershire, on the Churn, an upper branch of the Thames, and on the Thames and Severn canal, 17 m. s.e. of Gloucester. It has four chief streets, and the appearance of opulence, though it has but little trade. A complete agricultural college was founded here in 1846 on a farm of 600 acres. Pop. '71, 7,681. C. returns one member of parliament. C. was the Roman Corinium-Ceaster, at the junction of five Roman roads, and has traces of ancient walls 2 m. in circuit. Roman relics have been found here, as coins, urns, baths. Canute held a council here in 1020 to expel Ethelwolf. Rupert stormed C. in 1642 and 1643, and it was afterwards given up to Essex.

CIRILLO, DOMENICO, 1734–99; a Neapolitan naturalist who accompanied lady Walpole to France and England, and became a fellow of the royal society, enjoying there and on the continent the friendship of Buffon, Diderot, D'Alembert, and other learned men. When the French established government in Naples in 1799, C. was chosen a representative, and became president of the legislative commission. After the re-establishinent of the royal government, he was sentenced to death, but was offered his life if he would ask for mercy. This he refused to do, and suffered death. He wrote works on botany and entomology.

CIRRHOP'ODA, or CIRRIP'EDA (Gr, or Lat. cirrhus-footed), the animals which formed the genus lepas of Linnæus, ranked by him among the multivalve testacea, and by suhsequent naturalists very generally regarded as an order of mollusks, until, in consequence of recent discoveries, a place has been assigned them among the articulata, either as a distinct class of that great division of the animal kingdom, or as a sub-class of crustacea. Barnacles (q.v.) and balani or acorn-shells (see BALANUS) are the most familiar examples of C.; but many species are now known, all exhibiting much general similarity to these, all marine, and all in their mature state permanently attached to objects of various kinds, as rocks, sea-weeds, shells, etc. Some are found imbedded in corals, others in the thick skin of whales, some in the flesh of sharks. They are distributed over the whole world; the species, however, are not numerous anywhere; those species which adhere to fixed bodies are in general much more limited in their geographic range than those which attach themselves to floating objects or to vertebrate animals. They are generally divided into two orders, pedunculated and sessile, those of the former order being supported on a flexible stalk, which is wanting in the latter. Barnacles are pedunculated C., and balani are sessile.

The resemblance of C. to mollusks consists chiefly in their external appearance. In the more important parts of their organization, however, the C. resemble crustaceans rather than mollusks. The gills, when these exist, occupy the same relative position as in crustaceans; but the aëration of the blood is supposed to be also effected in the cirrhi, as the limbs or organs have been generally called, of which there are six pair on cach side, and which may be described as long tapering arms, each composed of many joints and ciliated or fringed with stiff hairs. The cirrhi nearest the mouth are shortest, and all of them together form a sort of net for the capture of minute animals, being incessantly thrown out by the cirrhopod from a lateral opening of its sac, and drawn in again in such a manner as to convey any prey which they may have caught to the mouth. Almost all the C. are hermaphrodite; but in a few genera the sexes are distinct, and these exhibit an anomaly of a very remarkable kind, the males being not only very small in comparison with the females, and more short-lived, but, in their mature state, parasitic on the females, or attached to them as they are to other objects; whilst in some the still more remarkable anomaly appears of what have been called complemental males, attached

Cissampelos.

in this way to hermaphrodites. The eggs of C. are hatched before being finally set free from the body of the parent. The young possess the power of locomotion, swimming freely in the water, and are furnished with eyes, which disappear after they have permanently fixed themselves, by instinctive choice, in situations adapted to their kind. They have also shells, quite different from those of their mature state. The shelly coverings of the C. are all formed according to a certain type, but with many variations, and they differ extremely in the number of pieces or valves of which they consist, some, as the common barnacles, having only tive valves, and others having additional small pieces arranged in whorls, and exceeding 100 in number. In most of the C., the shelly covering is very complete; in some, it is almost rudimentary.

The most important discoveries concerning the structure and metamorphoses of the C., determining their place in the animal kingdom, were made by Mr. J. V. Thompson. For the most extended examination of species, and for an admirable monograph, published by the Ray society, the scientific world is indebted to Mr. Darwin.

CIR'RHUS, CIR'RUS (Lat. a curl, or lock of hair), or TENDRIL, in botany, a leaf altered into a slender spiral, which, by twisting around such objects as it comes in contact with, attaches the plant to them, and enables it to climb, when otherwise, through the weakness of its stem, it must have been prostrate. There are many varieties of C., as it is merely an elongation of the midrib of a pinnate leaf—an altered terminal leaflet, or becomes compound by the alteration of several leaflets, or occupies altogether the place of a simple or compound leaf, and is accordingly either simple or branching. Examples of different kinds may be seen in the pea, vetch, vine, passion-flower, etc.— The term C. is also employed in zoology, to designate any curled tilament, and has been applied, but not quite aptly, to the curiously modified feet of the cirrhopoda.

CIRRUS, See CLOUDS.

CIRTA, an ancient city of Numidia, Africa, in the country of the Massyli, regarded as the strongest position in Numidia. It was the center of all the Roman military roads. It was restored by Constantine, and the modern town now bears his name.

CIS, a Latin preposition meaning, "on this side,” which is often prefixed to names of rivers and mountains to form adjectives; Cisalpine, Cispadane, “on this side of the Alps,” “of the Po.” As most of these words are of Roman origin, Rome is considered the point of departure.

CISAL'PINE REPUBLIC. After the battle of Lodi, in May, 1796, gen. Bonaparte proceeded to organize two states--one on the s. of the Po, the Cispadane republic, and one on the n., the Transpadane. These two, however, were in 1797 united into one under the title of the C. R., which embraced Lombardy, Mantua, Bergamo, Brescia, Cremona, Verona, and Rovigo, the duchy of Modena, the principality of Massa and CarTara, and the three legations of Bologna, Ferrara, and the Romagna. The republic had a territory of more than 16,000 sq.m., and a population of 34 millions. Milan was the seat of the government or directory, and the place of meeting of the legislative assembly, which was composed of a senate of 80 members, and a great council of 160. The army consisted of 20,000 French troops, paid by the republic. A more intimate connection was formed in 1798 between the new republic and France, by an alliance offensive and defensive, and a treaty of commerce. The republic was dissolved for a time in 1799 by the victories of the Russians and Austrians, but was restored by Bonaparte, after the victory of Marengo, with some modifications of constitution and increase of territory. In 1802, it took the name of the Italian republic, and chose Bonaparte for its president. A deputation from the republic in 1805 conferred on the emperor Napoleon the title of king of Italy; after which it formed the kingdom of Italy till 1814.

CISLEITHANIA, or CISLEITHIAN AUSTRIA, a name applied to that portion of the Austro-Hungarian monarchy which is represented in the Reichsrath of Vienna. It has about one balf the area and four sevenths of the population of the monarchy, and embraces the crown lands once belonging to the German confederation, Dalmatia, Buckowma, and Galicia.

CISPADANE REPUBLIC. See CISALPINE REPUBLIC, ante.

CIS'PLATINE REPUBLIC, the name of the republic of Uruguay, 1829–31. It had previously belonged to Brazil and had the name of the Cisplatine province.

CIS RHENANE REPUBLIC, the name chosen in 1797 for the proposed confederation of the German towns w. of the Rhine. As the whole region was soon afterwards transferred to France, the name never came into use.

CISSAM'PELOS (Gr. ivy-vine), a genus of plants of the natural order menispermacem, of which some of the species possess valuable medicinal properties; particularly C. pareira, a native of the West Indies and warm parts of America, the root of which is known by the names of pareira braxa and butua root. The plant is called velvet leaf in the West Indies, from the peculiar and beautiful appearance of the leaves. It is a climbing shrub, with roundish-triangular leaves, racemes of small yellow flowers, and small hairy scarlet berries. The root appears in commerce in pieces of 2 or 3 ft. long, varying from the thickness of the finger to that of the arm, tough, but so porous that air can be blown from end to end of it. It has a sweetish, afterwards nauseous taste; is used as a tonic

« AnteriorContinuar »