I shall not here enter into the causes of these effects, but indicate the conjectures which readily present themselves. We know from experience that animals or vegetables transplanted from a distant climate frequently degenerate, and sometimes are improved in a short time. It is easy to conceive, that this effect is produced by the difference of the climate and food. The influence of these two causes must at length render these animals exempt from, or susceptible of, certain affections or certain disorders; their temperament must gradually change; consequently their form, which depends partly on the food and the quality of the humours, must also change in their progeny. This change is indeed almost imperceptible in the first generation, because the male and female, supposed to be the stock of this race, being completely grown, had taken their consistence and form before they were brought from their own country; the new climate, and new food may, indeed, change their temperament, but cannot have influence enough on the solid parts, and organs to alter their form, consequently the first generation will be no ways changed, nor will the original stock at the time of birth be degenerated: but the young and tender animal will feel the influence of the climate, and receive a stronger impression than its father and mother had done. The food will also have a greater effect, and act upon the organic parts during the time of its growth, change a little the original form, and produce therein those seeds of defects which manifest themselves in a very conspicuous manner in the second generation, where the progeny will not only have its own defects which arise from its growth, but also the vices of the second stock. In the third generation, the defects, which proceed from the influence of the climate and food, combined with those of influence on the actual growth, will become so visible, that the character of the first stock will be effaced. Thus animals of a foreign race soon lose their particular qualities, and in every respect resemble those of the country. Spanish or Barbary horses, if the breed is not crossed frequently, become in France, French horses, in the second generation, and always in the third. We are, therefore, obliged to cross the breed instead of preserving it, and renew the race at each generation, by giving the horses of Barbary or Spain, to the mares of the country; and what is more singular, this renewal of the race, which is only done in part, produces much better effects than if the renewal was entire. A Spanish horse and mare in a foreign country do not produce such handsome horses as those which are bred from a Spanish horse and a mare of the country; this is easy to be conceived, if attention is given to the amendment of natural defects, which will be produced when a male and female of different countries are put together. Each climate, by its influence, and by that of its food, gives a certain conformation of