G4 P H Y P I A Organic acids, 52. ,, substance in plants, 47, 50. Organs, 10, 44. bilateral, 5S, 59. ,, dorsi ventral, 58, 59 ,, orthotropic, 61. plagiotropic, 61. ,, ra lial, 58, 50. terminal, 27. Osmosis, 44. Oxidation, of body, 0. in plants, 51. Oxygen in plants, 45, 62. Peripheral impressions, 39. rflu ger s law of contraction, 24. Physiology, definition of, 8. " methods of, 22. ,, problems of, 9, 16. Pillars of fornix, 31. INDEX TO PHYSIOLOGY (continued). Plastic products, 51, 54. Puns Varolii, 32, 36. Primordial utricle, 44. Proteids, 54. Protoplasm, 12, 21. ,, assimilation of, 13. ,, of plants, 43 Protoplasmic theory, 12 Pnlvinus, 63. Reetipetality, 58. Reflex actions, 28, 29. centres, 35, 36. Reserve materials, 54, 55. Respiration. 51. Root, structure of, 40. Root-hairs, 44, 46. Root-pressure, 46. Secretion, 11, 17, 18. Semicircular canals, 38. Sensory centres in brain-cortex, 41. ,, nerves, 8, 25. Simiatotropisni, 60. Spinal cord, physical anatomy of, ".4. as reflex centre, 35. ,, ,, as transmitter of nervous impressions, 34. ,, ns trophic centre, 35. ,, nerves, 4;t. Starch in plants, 54. Stimuli, of nerves, 24 sij. ,, of plant-movement, Stomata, 45 ;. Sympathetic system, 43. Temperature, influence of on growth of plants, 57. inflnenceof on movement of plants, 62. Tendrils, twining of, 00. Tetanus, 25. Thermotropism, 59. Tissues, 12. ,, constitution of, 16. Transpiration, 4c>. ,, current of, 47. Unipolar excitation, 25. Vacuole, 44. Vagi electrotonus, 25. Vascular system, li>. Vaso-inhlbitory nerves, 30. Vaso-mntor fibres, 30. Velocity, measurement of in nerves, Vital spirits, 10. Waller s law, 26. Waste-products, 51, 54. Water-culture, 48. White matter of nerves, 28, 35. PIACENZA (Fr., Flaisance ; Lat., Placentia), a city of Italy, a bishop s see, and the chief town of a province, lies on the Lombard plain, 217 feet above sea-level, not far from the right bank of the Po, just below the confluence of the Trebbia. By rail it is 43 miles south-east of Milan and 3-H north-west of Parma. Formerly a place of con siderable strength, it is still surrounded by walls with bastions and fosse in a circuit of 4 miles. The cathedral w r as erected between 1122 and 1233, in the Lombardo- Gothic style, under the direction of Santo da Sambuceto, on the site of a church of the 9th century which had been destroyed by earthquake. The west front has three doors with curious pillared porches. The campanile is a massive square brick tower 223 feet high ; the iron cage attached to one of its windows was put up in 1495 by Ludovico il Moro for the confinement of persons guilty of treason or sacrilege. The crypt is a large church supported by one hundred columns. Sant Antonino, which was the cathedral church till 877, and occupies the spot where it was reputed that St Barnabas preached to the people, was built by St Victor, the first bishop of Piacenza, in 324, restored in 903, rebuilt in 1104, and altered in 1857. It was within its walls that the deputies of the Lombard League swore to the conditions of peace ratified in 1183 at Constance. The brick vestibule (II Paradiso) on the north side is one of the older parts of the building. San Francesco, a spacious edifice begun by the Franciscans in 1278, occu pies the site of Ubertino Landi s palazzo, and is famous as the place where Agostino Landi harangued the people after the murder of Pierluigi, and where in 1848 the deputies of Piacenza proclaimed the annexation of their city to the Sardinian kingdom. San Sisto, which dates from 1499, and takes the place of the church founded in 874 by Angilberga (consort of the emperor Louis II.) for the Benedictines, lost its chief attraction when Raphael s Sistine Madonna (now in Dresden) was sold by the monks in 1754 to Frederick Augustus III. San Sepolcro and Sta Maria della Campagna are both after Bramante s designs ; the latter is rich in works of Pordenone. Sant Anna, dating from 1334, was the church of the barefooted Carmelites. Of the secular buildings in the city the most interesting is the Palazzo Communale, begun in 1281. In the main front the lower story, constructed of red and white marble, presents a series of five open pointed arcades ; tha upper story, in brick, has six very rich round-arched windows, each of five lights ; and above the cornice rise forked battlements. The square in front is known as the Piazza dei Cavalli, from the two bronze equestrian statues of Ranuccio (1620) and his father Alexander, prince of Parma, governor of the Netherlands (1G25). Both were designed by Francesco Mocchi. The Farnese palace was begun after Vignola s designs by Margaret of Austria in 1558 ; but it was never completed, and since 1800 it has been used as barracks. Other buildings or institutions of note are the old and the new bishop s palace, the fine theatre designed by Lotario Tomba in 1803, the great hospital dating from 1471, the library presented to the commune in 1846 by the marquis Ferdinando Landi, and the Passerini library founded in 1685. About a mile to the east of the city is the Collegio Alberoni, instituted in 1751 for the education of priests and missionaries. At a distance of about 2 miles in the opposite direction the Trebbia is crossed by a bridge of twenty-three arches, erected in 1825 at a cost of 47,000 ; the Austrians blew up two of the arches in 1859. Piacenza is an important point in the Italian railway system the Lombardy, Pied mont, and Ligurian lines meeting there with those of Central Italy. Silk, cotton, and woollen goods, pottery, and hats are among the local manufactures. The popula tion of the commune (which in this case is almost exactly identical with the city) was 34,985 in 1871 and 34,987 in 1881. Piacenza, originally, it is supposed, a Ligurian ami afterwards a Gallic town, was made a Roman colony in 219 n.c. While its walls were yet unfinished it had to repulse an attack by the Gauls, whose hopes were excited by the news of Hannibal s approach, and in the latter part of 218 it afforded protection to the remains of the Roman army under Scipio which had been defeated by the Carthaginian general in the great battle on the Trebbia. In 207 it withstood a protracted siege by Hasdrubal, Hannibal s brother, and thus contributed largely to the ultimate success of the Romans. Seven years later the Gauls surprised and burned the city ; and the colony was so diminished in strength that in 190 it had to lie recruited with three thousand families. In 187 it was connected with Rimini and the south by the construction of the jEmilian Way. During the later republic and the empire 1 lacenti.i is named in connexion with a defeat of the forces of Marius in the neighbourhood (82 B.C.), a mutiny of Julius Casar s garrison (49 B.C.), another mutiny under Augustus (41 B.C.), the defence of the city by Spurinna, Otho s general, against Ca cina, Yitellius s general (69 A. n. ), and the defeat of Aurelian by the Marcomanni outside the walls (271 A.D.). In 546 Totila reduced Piacenza by famine. Between 997 and 1035 the city was governed by its bishops, who had received the title of count from Otho III. In the latter part of the 12th century it was one of the leading members of the Lombard League. For the most part it remained Guelph, though at times, as when it called in Galcazzo Visconti, it was glad to appeal to a powerful Ghibelline for aid against its domestic tyrants. In 1447 the city was captured and sacked by Francesco Sforza. Having placed itself directly under papal protection in 1512, it was in 1545 united with PARMA (q.v.) to form an hereditary duchy for Pierluigi Farnese, son of Paul III. In 1746 a battle between the Franco-Spanish forces and the Austrians was fought under the city walls. In 1 848 Piacenza was the first of the towns of Lombardy to join Piedmont ; but it was re-occupied by the Austrians and had to wait for its emancipation till 1859. Lucius Calpurnius Piso (father-in-law of Julius Ca sar), Pope Gregory X., and Alexander Farnese, duke of Parma, were natives of the city. Among the local historians are Boselli, Rossi, IJonara, and Gemini. PIANOFORTE. The group of keyed stringed instru ments, among which the pianoforte is latest in order of time, has been invented and step by step developed with the modern art of music, which is based upon the simul
taneous employment of different musical sounds. In the