Page:The New International Encyclopædia 1st ed. v. 13.djvu/712

* MITOSIS. 634 MITRE. successive series of cells during gro«-th. By the time llie process has leaclieil tlu!- >tage a si)ecial mcclianism appears, which has till now remained concealed in the cell-substance. This serves to divide the chromatin elements into two equal parts, to separate the resulting halves from one another, and to arrange them in a regular man- ner. At the opposite poles of the longitudinal a.is of the nucleus two clear bodies — the 'cen- trosomes,' each surrounded by a clear zone, the so-called 'sphere of attraction' — now become visi- ble. These were first discovered by Fol, by Van Beneden, and also by Boveri, who recognized their importance. They appear to possess a great power of attraction over the vital particles of the coll, so that those become arranged around them like a series of ra,vs. At a certain stage in the ])roparation for division, the substance of the cell- body and of the nucleus gives rise to delicate fibres or threads; these fibres are motile, and, after the disappearance of the nuolcar mem- brane, seize the chromosomes with wonderful cer- tainty and regularity, and in such a way that each element is held on either side by several threads from each jiole. The chromatin elements thus immediately become arranged in a fixed and regular manner, so as to lie in the equatorial plane of the nucleus. The centrosomes and threads or astral fibres (axlei') called the '.spin- dle' together form the 'am pinaster.' The chro- matin olemonts next split longitudinally, thus becoming douljlod. as discovered by Fleming. This splitting is completed by the two halves being gradually drawn farther apart toward the op- posite poles of the nuclear spindle, until they finally approach the centre of attraction or oen- trosome, which has now fulfilled its object for the present, and retires into the obscurity of the cell- substance, only to booome active again at the next cell division. Kach .separate half of the nucleus now ''onstitutes a daughter nucleus in whiih it breaks up. and is scattered in minute granules in the nuclear network. The body of the cell then divides, showing two new cells. Eou.x has pointed out that the whole complex but wonderfully exact apparatus for the division of the nucleus exists for the purpose of divid- ing the chromatin Bubstancc in a fi.ed and regu- lar manner, not merely <|Uanlitatively, but also in respect of the dilVeront qualities which nuist be contained in it. It will l>e remembered that the chromatin particles or chromosomes are be- lieved to be bearers of hcreditv. The mechanism of mitosis is thus far unkno«Ti. The problem may be solved, as Wilson states, through chemi- cal research. Amitosi.s. ^litosis is the indirect division of the nucleus: where the nucleus elongates and di- rectl.v divides through its total mass the process is called 'amitosis.' This appears to occur ex- cept iunall.v. but is known to take phue in auKoba, in leucoc.vtes, and has boon observed in the sperm-cells and eggs of batracbians and some in- sects; but more commonl.v in pathological tissues. Bliii.lo<iH,PliY. Fleming, Zrllxuh.ilnnz, Kern vnd Zcllleiliiiitf (Leipzig. 1S82) ; Roux, I'cher <lir lirrleiiliinfi ilrr Ki rntriliinfi-ififttircii (Leipzig, 188.3); (Irsiimiiirltr .bhamlluiir/rn iihrr I'nI- irirJ.Jitnpsnirchnnik tjrr Orrintiisnirn (Leipzig, 18'X")) ; Weisniann, Thr flrrm I'titsm (Xow York, 18031 ; Wilson, rii,' Crll iu Drrrlnpment and In- hrritnncr ( Xew York. IS'IO). See CELL; Embby- OLOCT; JIeCHAMCS of DEVELOPMENT. MITRA (Skt., friend). A 'edic Hindu deity. He is mentioned most frequently in cipiiipany with 'aruna (ci-v.), with whom in the Veda liis at- tributes l)lend. Although he seems to have been a god of importance in the Indo-lranian religion, he lost his rank early in the Indian period, and was not recognized after the Vedic age. His Iranian counterpart, ilithra (q.v. ), however, was one of the chief deities of the pre-Zoroastrian religion, where lie represented the sun. MITRAILLEUSE, m^'tri'yCz' (Fr. mitraille- firer, from iiiitydiller, to fire mitraille, from mi- iruillc, liits of grape-shot, from OF. titituilU . frag- ments, from mile, small bit: ultimately connected with (iotli. mnitan, to cut). A machine gun, in which is combined a number of rifle barrels, with breech-action mechanism, and designed to dis- charge small missiles with great rapidity. It was invented in Belgium, and adopted Ijy the French a little before the war with Germany in 1870. See ilAciiixK lU x.s. MITRAL VALVE. Sec Heart; Circul.- TIOX. MITRE (OF.. Fr. mitre, from Lat. mitra, from Gk. fiirim, mitre, fillet, bell ; probably ulti- matel.v of Oriental origin). The head-dross worn in solemn functions by bishops and some abbots. The ornament is ])rol)ably of Eastern origin, al- though the head-dress of Eastern ])relatos at the present d;i.v is quite different, lieing a large round cap. something like a crown. Tlie Western mitre is a tall, tongue-shaped cap, terminating in a two- fold i)oint, .supposed to s^'mlxdize the 'eloven tongues as of fire' in which the Holy Spirit de- soenilod upon the Apostles ; two Haps or stream- ers fall from it behind over the shoulders. Opin- ion is much divided as to the date at which the mitre first came into use. Eusoliius. Gregory Xaziinzen, Epiphanius, and others s]ieak of an ornamented head-dress worn in the (buroh: Imt there is no vcr.v early pictorial representation which exhibits an.v head-covering at all resembling the modern mitre. From the tenth century, how- ever, it is undcnd)tedl,v found in use, altlumgh not at first iniversall.v. At the Reformation the mitre was practically discarded as a jiart of the epis- copal costume in England, though there arc traces of its survival in iscdatod instances; and the first Bishop of the Episocijial Church in America, Soabury, occasionally wore one. In the last half of the nineteentli (•entury the practice was revived with increasing frequency in the Anglican Communion. In the Roman Catholic ritual throe kinds of mitres are distinguished: mitra preliosa, richly ornamented with jewels, gold, and silver; mitra (luriphri/fiiala. of gold brnc:ule with embroidery; and mitra simptex. of white silk or linen damask, with soarcol.v any decoration, which is worn when black vestments are used. See Costime, Ecclesiastical. MITRE, me'trA. BARTOLOMfi (1S2I — ). . Argentine statesman, born at Hucnos Avros. To escape the despotism of the Dictator Rosas, he lied to Montevideo. In IStfi he emigrated to Bolivia, where he was appointed ehief of staff to President Ballivian. and director of the military college. l'])on the overthrow of liallivian (1847) ho was banished tii Peru, and thence went to Chile. In 18.51 he joined I'rquizii in the upris- ing against Rosas, ami in I8."i'2 commanded the revolutionary artillery at the battle of Monto Caseros, in which Rosiis was overthrovn. Elected