opinions. The authority of experienced observers, even when they do not
advance the grounds of their belief, is of some little value. Now almost all
men who have bred many kinds of animals and have written on the subject, such
as Sir J. Sebright, Andrew Knight, etc. (17/3. For Andrew Knight see A. Walker
on 'Intermarriage' 1838 page 227. Sir J. Sebright 'Treatise' has just been
quoted.), have expressed the strongest conviction on the impossibility of
long-continued close interbreeding. Those who have compiled works on
agriculture, and have associated much with breeders, such as the sagacious
Youatt, Low, etc., have strongly declared their opinion to the same effect.
Prosper Lucas, trusting largely to French authorities, has come to a similar
conclusion. The distinguished German agriculturist Hermann von Nathusius, who
has written the most able treatise on this subject which I have met with,
concurs; and as I shall have to quote from this treatise, I may state that
Nathusius is not only intimately acquainted with works on agriculture in all
languages, and knows the pedigrees of our British breeds better than most
Englishmen, but has imported many of our improved animals, and is himself an
experienced breeder.

Evidence of the evil effects of close interbreeding can most readily be
acquired in the case of animals, such as fowls, pigeons, etc., which propagate
quickly, and, from being kept in the same place, are exposed to the same
conditions. Now I have inquired of very many breeders of these birds, and I
have hitherto not met with a single man who was not thoroughly convinced that
an occasional cross with another strain of the same sub-variety was absolutely
necessary. Most breeders of highly improved or fancy birds value their own
strain, and are most unwilling, at the risk, in their opinion, of
deterioration, to make a cross. The purchase of a first-rate bird of another
strain is expensive, and exchanges are troublesome; yet all breeders, as far
as I can hear, excepting those who keep large stocks at different places for
the sake of crossing, are driven after a time to take this step.