The Principles of Breeding | Page 8

in this way are liable to fall an easy prey to any ordinary or prevailing disease which develops in such with unusual severity. Sheep are also liable to several diseases of the brain and of the respiratory and digestive organs. Epilepsy, or "fits," and rheumatism sometimes occur.
Swine are subject to nearly the same hereditary diseases as sheep. Epilepsy is more common with them than with the latter, and they are more liable to scrofula than any other domestic animals.
When properly and carefully managed, swine are not ordinarily very liable to disease, but when, as too often kept in small, damp, filthy styes, and obliged constantly to inhale noxious effluvia, and to eat unsuitable food, we cannot wonder either that they become victims of disease or transmit to their progeny a weak and sickly organization. Swine are not naturally the dirty beasts which many suppose. "Wallowing in the mire," so proverbial of them, is rather from a wish for protection from insects and for coolness, than from any inherent love of filth, and if well cared for they will be comparatively cleanly.
The practice of close breeding, which is probably carried to greater extent with swine than with any other domestic animal, undoubtedly contributes to their liability to hereditary diseases, and when those possessing any such diseases are coupled, the ruin of the stock is easily and quickly effected, for as already stated, they are propagated by either parent, and always most certainly and in most aggravated form, when occurring in both.
With regard to hereditary diseases, it is eminently true that "an ounce of prevention is worth a pound of cure." As a general and almost invariable rule, animals possessing either defects or a tendency to disease should not be employed for breeding. If, however, for special reasons it seems desirable to breed from one which has some slight defect of symmetry, or a faint tendency to disease, although for the latter it is doubtful if the possession of any good qualities can fully compensate, it should be mated with one which excels in every respect in which the other is deficient, and on no account with one which is near of kin to it.
Notwithstanding the importance due to the subject of hereditary diseases, it is also true that few diseases invariably owe their development to hereditary causes. Even such as are usually hereditary are sometimes produced accidentally, (as of course there must be a beginning to everything,) and in such case, they may, or may not be, transmitted to their progeny. As before shown, it is certain that they sometimes are, which is sufficient reason to avoid such for breeding purposes. It is also well known that, in the horse, for instance, certain forms of limbs predispose to certain diseases, as bone spavin is most commonly seen where there is a disproportion in the size of the limb above and below the hock, and others might be named of similar character; in all such cases the disease may be caused by an agency which would be wholly inadequate in one of more perfect form, but once existing, it is liable to be reproduced in the offspring--all tending to show the great importance of giving due heed in selecting breeding animals to all qualities, both external and internal, so long as "like produces like."
FOOTNOTES:
[2] Finlay Dun, V.S., in Journal of the Royal Agricultural Society.
CHAPTER III.
THE LAW OF VARIATION.
We come now to consider another law, by which that of similarity is greatly modified, to wit, the law of variation or divergence. All organic beings, whether plants or animals, possess a certain flexibility or pliancy of organization, rendering them capable of change to a greater or less extent. When in a state of nature variations are comparatively slow and infrequent, but when in a state of domestication they occur much oftener and to a much greater extent. The greater variability in the latter case is doubtless owing, in some measure, to our domestic productions being reared under conditions of life not so uniform, and different from, those to which the parent species was exposed in a state of nature.
Flexibility of organization in connexion with climate, is seen in a remarkable degree in Indian corn. The small Canada variety, growing only three feet high and ripening in seventy to ninety days when carried southward, gradually enlarges in the whole plant until it may be grown twelve feet high and upwards, and requires one hundred and fifty days to ripen its seed. A southern variety brought northward, gradually dwindles in size and ripens earlier until it reaches a type specially fitted to its latitude.
Variation, although the same in kind, is greater in degree, among domesticated plants than among animals. From the single wild variety of the potato as first discovered and taken to Europe, have sprung