Acclimation, Or Acclimatization, the process by which an individual or a species, on being removed to a different climate, becomes modified in constitution and adapted to the changed conditions. The two words, however, are not strictly synonymous. Acclimation is generally used in speaking of particular individuals, and more especially of those belonging to the human species, and refers to the alterations which the system undergoes spontaneously in a foreign climate, by which it at last becomes no longer subject to the maladies peculiar to new-comers. Acclimatization, on the contrary, expresses the artificial care by which man succeeds in naturalizing, under his own supervision, a species of animals or vegetables of exotic origin. - Acclimation. Man inhabits all the zones and nearly every region of the earth, and has been enabled in repeated migrations to change the place of his habitation and to occupy new countries. The human species is therefore regarded as cosmopolitan; and yet two facts are important to notice in this respect: First, most of the great migrations, historic or traditional, have been made in the direction of longitude and not in that of latitude; the migrating tribes instinctively or intentionally keeping nearly within the same parallels of latitude, and consequently not suffering very great alterations of temperature, nor meeting in their new homes with a flora and fauna very dissimilar to those of their native country.

Secondly, at the present day, although an individual may migrate either westward or eastward, as a general rule, without suffering from the change, a removal into a different latitude is almost always accompanied with peculiar dangers during the first few years of his residence in the new locality. The most marked instance of this kind is when a person from the temperate zone visits for the first time a tropical or subtropical region. The dangers that first beset him arc fevers, which are so marked in type and so ready to attack newly arrived immigrants, that they are sometimes called the " strangers' fever." The yellow fever of the West Indies and the southern United States, and the coast fever of western Africa, are well known examples of these affections. They are not absolutely restricted to new-comers, the natives being also subject to them; but the recent immigrant is so much more likely to be affected, and is attacked by the disease in so much larger proportion, it is evident that his system has in it something which offers a peculiar attraction for the febrile poison, and which does not exist, at least to the same extent, in that of the native or the old resident.

After passing through a period of general ill health and debility, extending over some years, and perhaps one or more severe at-tacks of illness, the immigrant approximates in his appearance and habit of body to the older denizens of the place, and is no longer peculiar-ly liable to the disorders which affected him on his arrival. He is then said to be acclimated. No doubt, part of the immunity enjoyed by old settlers in a tropical or sub-tropical climate is due to the fact that they have learned prudence in regard to exposure, and have come to regulate habitually their mode of life to cor-respond with the climate of the country. Re-cent immigrants often neglect these essential precautions, because they have not found them necessary in a temperate climate; and it is only after repeated experience of their value that they come to adopt them habitually and as a constant protection. - Acclimatization. Many of the useful animals and plants have been successfully transferred from their original lo-cality and made to thrive in new and unaccus-tomed places. The horse, the ass, the ox, the sheep, the goat, and the cat have accompanied man nearly everywhere within the temperate and tropical regions, and the dog is his companion even within the arctic circle.

This fact has given rise to the hope that acclimati-zation might be successfully extended to still other species, and the societe d'acclimcitation at Paris has been established with a view of experimental investigation in this direction. Their endeavors have in many instances proved successful, at least in so far that tropical animals are found, when well cared for, to support the cold of a European winter without injury or even inconvenience. The zebra from Africa may be seen quietly resting upon the snow, and the tapir from Guiana swimming for his amusement in the stream which runs through his enclosure, when the temperature of the water is hardly above the freezing point. This, however, by no means indicates a completely successful ac-climatization. It is successful so far as the individual is concerned; but acclimatization means the survival and prosperity of the species. In order to secure this result, the animals which have been imported must themselves thrive and reach their usual term of existence, and produce offspring; the parent must willingly take the natural care of her young; the young animals must themselves have sufficient vigor to arrive at maturity and again reproduce their kind.

Either one of these conditions may fail, and in certain instances have done so, notwithstanding that all the preceding ones had fully succeeded. Finally, in order that acclimatization may be in any case practically useful, the animals of the naturalized species must, in addition, be able in their new habitation to bear the labors or produce the material for the sake of which man has taken them under his care. Plants may be acclimatized to a certain extent, and if slowly accustomed to a change of climate, and well cared for, they will in their offspring undergo changes which will fit them for the new conditions under which they live. Experiments in this direction have in some instances met with unexpected success; and on the ground of this, societies have been formed in some of the principal European cities to accomplish the acclimatization of sub-tropical and some tropical plants to their latitude, and also of those belonging to colder regions.