The effects of acclimatisation (the process of inuring an animal to a foreign climate) may be divided into (1) those produced on the emigrant, and (2) those made manifest in its descendants; the latter changes being much better marked than the former. Whether the new climate be bad or good, its influence on the progeny of imported stock tends to render them like unto the type peculiar to the adopted country. Thus, the English-bred offspring of Arabs lose, even in the first generation, a large portion of the characteristics which distinguish the sons and daughters of the Desert; and in India, English blood quickly assumes a "country-bred" appearance. The effects of soil and climate in developing special equine types may be easily seen by comparing even Irish with English horses, or Shires bred in Norfolk with those produced in the Midlands, to say nothing of comparisons made between Australians and Arabs, for instance. Horses and their progeny support in an admirable manner a change from a hot or temperate climate to a cold one, such as that from Arabia to Russia, where the Arab Smetanka, imported in 1775 and united with Danish, Dutch and English mares, was the founder of the famous breed of Orlof trotters. The hardy and well-shaped remounts which are bred in the bitterly cold steppes of the Don and Volga, are to a large extent Anglo-Arabs. Many of the excellent saddle horses of Montana are pure or nearly pure English. A change from a cold or temperate climate to a very hot one is, on the contrary, badly borne, at least by the descendants, and especially if the new climate is damp as well as tropical. The heat of Queensland, where good horses are bred, might be taken as the maximum for successful breeding. In a climate as hot as India, it is impossible to continue to breed good stock, without frequent importations of fresh blood, and even then it is impossible to get a sufficiency of bone and substance for weight carrying and heavy draught purposes.

The accommodation of the system to new surroundings is well illustrated by the readiness with which the skin responds to the stimulus of cold, or to the sedative action of heat, in the growth of the epidermis. A striking instance of this fact is afforded by the change in the order of shedding the coat which takes place among Australian horses that are imported into India. These animals, which, in the Antipodes, get their winter coat in the spring, and their summer one in the autumn, at first suffer during the Indian hot months from wearing a coat which is abnormally heavy for the climate of their new place of residence. However, in a comparatively short time, say, in a couple of years, the order of shedding the coat changes to that of Indian horses, with an improved state of health.