There are numerous obstacles to the cultivation of this alpine tract. The intense cold of its winters, which exceeds that of any other country. From the snow lying so long on the ground, the parts exposed to the north are incapable of any culture. Frosts are frequent even in summer. The days are dark in winter. The weather is always moist. The soil is of a turfy kind, composed of mosses decayed by frost, impregnated with standing water. Good black vegetable mould is not to be met with. Lofty trees cannot be raised, on account of the excessive violence of the wind; hence there is a great scarcity of wood. It is customary for those in our part of Sweden who fancy themselves indisposed, to frequent watering-places, or mineral springs, during the heat of summer. For my own part, I have, thank God! for several years enjoyed tolerable health, except a slight languor, or other trifling indisposition. But as soon as I got upon the alps, I seemed to have acquired a new existence. I felt as if relieved from a heavy burthen; and after having spent a few days in the low country of Norway, though without having committed the least excess, I found my languor or heaviness return. When I again ascended the alps, I revived as before, to which the pure and well ventilated atmosphere did not a little contribute. It is a prevailing opinion that, at a great elevation, the air is so much thinner, as to render it necessary to breathe through wet sponges held to the nose and mouth. I can aver that the difficulty of breathing is only caused by the exertion of climbing the mountains, as a person who runs fast, or uses any other violent exercise, oppresses his lungs by accelerating the circulation of the blood.[64] [64] This opinion of Linnæus coincides with what M. de Saussure observed in ascending Mont Blanc. We cannot say so much in favour of his subsequent theory.