P occurs as an accompaniment or sequel of bronchitis either from the inflammation passing from the finer bronchi to the pulmonary air vesicles, or from its affecting portions of lung which have undergone collapse. It occurs most frequently in children, and is often connected with some pre-existing acute ailment in which the bronchi are implicated, such as measles or hooping cough. It likewise affects adults and aged people in a more chronic form as the result of bronchitis. Sometimes a condition of catarrhal pneumonia may be set up by the plugging of one or more branches of the pulmonary artery, as may occur in heart disease, pyaemia, &c. The symptoms characterizing the onset of catarrhal pneumonia in its more acute form are the occurrence during an attack of bronchitis of a sudden and marked elevation of temperature, to gether with a quickened pulse and increased difficulty in breathing. The cough becomes short and painful, and there is little or no ex pectoration. The physical signs are not distinct, being mixed up with those of the antecedent bronchitis ; but, should the pneumonia be extensive, there may be an impaired percussion note with tubular breathing and some bronchophony. Acute catarrhal pneumonia must be regarded as a condition of serious import. It is apt to run rapidly to a fatal termination, but on the other hand a favourable result is not (infrequent if it is re cognized in time to admit of efficient treatment. In the more chronic form it tends to assume the characters of chronic phthisis (see PHTHISIS). The treatment is essentially that for the more severe forms of bronchitis (see BRONCHITIS), where, in addition to expectorants, together with ammoniacal, ethereal, and alcoholic stimulants, the maintenance of the strength by good nourishment and tonics is clearly indicated. The breathing may often be re lieved by light warm applications to the chest and back. Con valescence is often prolonged, and special care will always be required in view of the tendency of the disease to develop into phthisis. Chronic Interstitial Pneumonia or Cirrhosis of the Lung is a slow inflammatory change affecting chiefly one portion of the lung texture, viz., its fibrous stroma. The changes produced in the lung by this disease are marked chiefly by the growth of nucleated fibroid tissue around the walls of the bronchi and vessels, and in the intervesicular septa, which proceeds to such an extent as to invade and obliterate the air cells. The lung, which is at first enlarged, becomes shrunken, dense in texture, and solid, any unaffected portions being emphysematous ; the bronchi are dilated, the pleura thickened, and the lung substance often deeply pigmented, especially in the case of miners, who are apt to suffer from this disease. In its later stages the lung breaks down, and cavities form in its substance as in ordinary phthisis. This condition is usually present to a greater or less j degree in almost all chronic diseases of the lungs and bronchi, but it is specially apt to arise in an extensive form from pre-existing catarrhal pneumonia, and not unfre- quently occurs in connexion with occupations which necessitate the habitual inhalation of particles of dust, such as those of colliers, flax-dressers, stonemasons, millers, &c. The symptoms are very similar to those of chronic phthisis (see PHTHISIS), especially increasing difficulty of breathing, particularly on exertion, cough either dry or with expectoration,* sometimes copious and fetid. In the case of coal-miners the sputum is black from containing carbonaceous matter. The physical signs are deficient expansion of the affected side the disease being mostly confined to one lung increasing dulness on percussion, tubular breathing, and moist sounds. As the disease proif! esses retraction of the side becomes manifest, and the Ljart and liver may be displaced. Ultimately the condition both as regards physical signs and symptoms takes the characters of the later stages of phthisis with colliquative symptoms, increasing emaciation, and death. Occasionally dropsy is present from the heart becoming affected in the course of the disease. The malady is usually of long duration, many cases remaining for years in a stationary condition and even undergoing temporary improvement in mild weather, but the tendency is on the whole downward. The treatment is conducted on similar principles to those applicable in the case of phthisis. Should the malady be con nected with a particular occupation, the disease might be arerted or at least greatly modified by early withdrawal from such source of irritation. (J. 0. A.) PNOM-PENH, the capital of CAMBODIA (see vol. iv. p. 725). PO, the largest river of Italy, traverses the whole length of the great plain between the Alps and the Apennines, which was in the Miocene period an arm of the sea con necting the Adriatic with the Mediterranean by what is now the Col d Altare or Col di Cadiboi:a and has gradually been filled by detritus from the surrounding highlands. That its course lies much nearer the Apennines than the Alps is evidently due to the fact that the tributaries from the loftier range on the north, whether in the form of glacier or stream, have all along been much more powerful than the tributaries from the south. The total length of the river from its conventional source to the mouth of the principal channel is 417| miles, and the area of its basin, which includes portions of Switzerland and Austria, is estimated at 26,798 square miles. The general course of the river has been already described in ITALY (vol. xiii. p. 435). The Po forms a very extensive delta, and is probably one of the most active of all rivers in the work of denuda tion. Prony has calculated that between 1200 and 1600 the delta advanced at the rate of 80 feet per annum ; and between 1600 and 1804 the rate is said to have been as much as 230 feet. This advance has naturally been attended by great changes in the course and size of the several channels. Piavenna, for example, once a great port, now stands on dry land 4 miles from the sea. The modern lagoons of Comacchio, Avhich stretch southwards from the delta, are being artificially reclaimed by the help of the alluvial deposits. In its ordinary condition the Po has a depth between Pancalieri and the mouth of the Ticino of from 6 to 10 feet, and between the mouth of the Lambro and that of the Adda of about 14 or 15 feet. Lower down the depth occasionally exceeds 40 feet. Permanent fords exist only in the upper Po, and between the mouths of the Ticino and the Lambro. In times of great drought _the bed is quite dry at Rovello, and fords appear below Casalmaggiore and at Borgo forte, where the French and Germans crossed in 1796, 1807, 1813, and 1814 ; but in general the river forms a complete barrier both to foot and horse. The principal points where crossing is effected by ferries or bridges are *Moncalieri, Turin, *Casale Monferrato, Frassinato, *Valenza, *Mezz;ma Corti, *Piacenza, Cremona, Casalmaggiore, Brescello, *Borgoforte, San Benedetto, Ostiglia, *0cchiobello, Pontelagoscuro, Francolino. Railway bridges exist at the places distinguished by an asterisk. The river in general is at its fullest in May and June, and at its lowest in January (see details in Lombardini s elaborate study on the lower Po in Memorie del Ecalc Istituto Lombardo, Milan, 1870). The ordinary floods on the Po are attended with little danger ; but at intervals sometimes of a few sometimes of many years they become events of the gravest national concern. Those of 1651 and 1705 are among the most destructive recorded in history, and in the present century the more memorable are those of 1839, 1846, 1855, 1857, 1868, 1872, and 1879. In 1872 1150 square miles of country between the Reno and the Adige were submerged, the district about Modena was turned into a lake, the people of Revere saved the rest of their town only by sacri ficing the front row of houses to form a temporary embankment, and it was only by the wisely conducted energy of its inhabit ants that Ostiglia was kept from destruction. During April and May 1879 the rainfall was exceptionally heavy, the quan tity for May alone being equal to more than a third of the an nual total. The result was a rise in all the tributaries of the Po, and on May 30 the flood in the main river was 21 feet above low water at M-czana Corta. A breach 720 feet long in the embank ment between Bonizzo and Borgofranco caused the submergence of 155 square miles in the provinces of Mantua, Modena, and Ferrara, and involved in its repair a national expenditure of 53,460. Of the 5,902,981 devoted by the Government to the regulation of the rivers of Italy in the twenty years 1861-1880, 2,257,872 had to be appropriated to the Po and its tributaries. Nowhere in Europe except in Holland has the system of embankment been carried to such perfection on so extensive a scale. A wide bed for the river at its height is enclosed for long distances by a massive master-dyke OT/roldo, and in the space between this and the ordi nary channels suitable areas are often enclosed by secondary dykes or golenc. The following figures show the extent of the system in
1880 :