It has long been a disputed point whether the system of breeding _in-and-in_ or the opposite one of frequent crossing has the greater tendency to maintain or improve the character of stock. The advocates of both systems are earnest and confident of being in the right. The truth probably is, as in some other similar disputes, that both are right and both wrong--to a certain extent, or within certain limits. The term _in-and-in_ is often very loosely used and is variously understood; some, and among these several of the best writers, confine the phrase to the coupling of those of exactly the same blood, i.e. brothers and sisters; while others include in it breeding from parents and offspring, and others still employ the term to embrace those of more distant relationship. For the latter, the term breeding in, or close breeding, is deemed more fitting. The prevalent opinion is decidedly against the practice of breeding from any near relationships; it being usually found that degeneracy follows, and often to a serious degree; but it is not proved that this degeneracy, although very common and even usual, is yet a necessary consequence. That ill effects follow in a majority of cases is not to be doubted, but this is easily and sufficiently accounted for upon other grounds. In a state of nature animals of near affinities interbreed without injurious results, and it is found by experience that where domesticated animals are of a pure race, or of a distinct, well defined and pure breed, the coupling of those of near affinities is not so often followed by injurious effects as when they are crosses, or of mixed or mongrel origin, like the great majority of the cattle in the country at large. In the latter case breeding in-and-in is _usually_ found to result in decided and rapid deterioration. We should consider also that few animals in a state of domestication are wholly free from hereditary defects and diseases, and that these are propagated all the more readily and surely when possessed by both parents, and that those nearly related are more likely than others, to possess similar qualities and tendencies.