It is subject, however, to extreme and rapid variations in temperature, to alternations of dry and humid winds (the latter, called catias, being irritating and oppressive), to chilling night mists brought up from the coast by the westerly winds, and to other influences productive of malaria, catarrh, fevers, bilious disorders and rheumatism.
Malarial fevers make their appearance in places where the forest has been recently felled, or where the surface earth has been disturbed.
The valley regions are tropical, and malarial fevers are common.
From the time of Hippocrates onwards the malarial or periodical fevers have engaged the attention of innumerable observers, who have suggested various theories of causation, and have sometimes anticipated - vaguely, indeed, but with surprising accuracy - the results of modern research; but the true nature of the disease remained in doubt until the closing years of the 19th century.
But while the province in many parts presents a landscape of luxuriant beauty, it is a prey to the ravages of disease, principally malarial fevers due to the extensive swamps formed by waters stagnating in the forests, and to the frequent incursions of the Goklan and Yomut Turkomans, who have their camping-grounds in the northern part of the province, and until about 1890 plundered caravans sometimes at the very gates of Astarabad city, and carried people off into slavery and bondage.