As regards the direction of the winds, the great plain bounded by the Apennines and the Alps resembles an Alpine valley, the winds either blowing up it from east to west, or in an inverse direction. The winds descending from the Alps rarely bring rain, for they have deposited their moisture on the western slopes, but those coming from the Adriatic are generally charged with moisture. Nevertheless, owing to the great extent of the plains and the numerous breaks in the mountain chains, this rule is frequently interfered with. In the Alpine valleys the ascending and descending currents are far more regular, and the navigators on the lakes fully avail themselves of this circumstance. The forty-fifth degree of north latitude intersects the valley of the Po, but the climate, nevertheless, is not as mild as might be expected from this circumstance, and the range of temperature is great. In the Val Tellina the temperature sometimes rises above 90°, and frequently fails below freezing point. In the plain the climate is less austere, but it is notwithstanding continental in its character; and Turin, Milan, and Bologna are for this reason the least pleasant cities of Italy to live in. A few favoured spots on the Alpine lakes, such as the Borromean Islands, are an exception to this rule, and enjoy an equable climate, thanks to the moderating influences of a vast expanse of water. In the Gulf of Pallanza the thermometer never falls below 40° F., and we must go as far as Naples if we would meet with a climate equally favourable to vegetation. Venice, too, is a privileged spot, thanks to the vicinity of the Adriatic, and is healthy, too, in spite of the lagoons {215} which surround it. It is remarkable that these brackish lakes and swamps of Northern Italy do not give rise to the dreaded malarial fevers. Venice undoubtedly owes its healthiness to the tides, which are higher there than in the Tyrrhenian Sea, and perhaps, also, to the cold winds descending from the Alps. Comacchio, too, is a healthy place, and young natives of the Polesina suffering from consumption are sent there to recover their health. Wherever the engineers have cut up the connection between the lagoons and the open sea, marsh fever has made its appearance. The swamps of Ravenna and Cervia breed malignant fevers, especially where avaricious landowners have cut down the protecting rows of pines and oaks. A heavy miasmal air hangs likewise over the environs of Ferrara and Malalbergo, at the head of the Paduan delta.