de la Soc. d'Acclimat.' 1860 page 477.) Nevertheless, most great breeders of sheep have protested against close interbreeding prolonged for too great a length of time. (17/12. Nathusius 'Rindvieh' s. 65; 'Youatt on Sheep' page 495.) The most celebrated of recent breeders, Jonas Webb, kept five separate families to work on, thus "retaining the requisite distance of relationship between the sexes" (17/13. 'Gardener's Chronicle' 1861 page 631.); and what is probably of greater importance, the separate flocks will have been exposed to somewhat different conditions.
Although by the aid of careful selection the near interbreeding of sheep may be long continued without any manifest evil, yet it has often been the practice with farmers to cross distinct breeds to obtain animals for the butcher, which plainly shows that good of some kind is derived from this practice. We have excellent evidence on this head from Mr. S. Druce (17/14. 'Journal R. Agricult. Soc.' volume 14 1853 page 212.), who gives in detail the comparative numbers of four pure breeds and of a cross-breed which can be supported on the same ground, and he gives their produce in fleece and carcase. A high authority, Mr. Pusey, sums up the result in money value during an equal length of time, namely (neglecting shillings), for Cotswolds 248 pounds, for Leicesters 223 pounds, for Southdowns 204 pounds, for Hampshire Downs 264 pounds, and for the crossbred 293 pounds. A former celebrated breeder, Lord Somerville, states that his half-breeds from Ryelands and Spanish sheep were larger animals than either the pure Ryelands or pure Spanish sheep. Mr. Spooner concludes his excellent Essay on Crossing by asserting that there is a pecuniary advantage in judicious cross-breeding, especially when the male is larger than the female. (17/15. Lord Somerville 'Facts on Sheep and Husbandry' page 6. Mr. Spooner in 'Journal of Royal Agricult. Soc. of England' volume 20 part 2. See also an excellent paper on the same subject in 'Gardener's Chronicle' 1860 page 321 by Mr. Charles Howard.)
As some of our British parks are ancient, it occurred to me that there must have been long-continued close interbreeding with the fallow-deer (Cervus dama) kept in them; but on inquiry I find that it is a common practice to infuse new blood by procuring bucks from other parks. Mr. Shirley (17/16. 'Some Account of English Deer Parks' by Evelyn P. Shirley 1867.), who has carefully studied the management of deer, admits that in some parks there has been no admixture of foreign blood from a time beyond the memory of man. But he concludes "that in the end the constant breeding in-and-in is sure to tell to the disadvantage of the whole herd, though it may take a very long time to prove it; moreover, when we find, as is very constantly the case, that the introduction of fresh blood has been of the very greatest use to deer, both by improving their size and appearance, and particularly by being of service in removing the taint of 'rickback,' if not of other diseases, to which deer are sometimes subject when the blood has not been changed, there can, I think, be no doubt but that a judicious cross with a good stock is of the greatest consequence, and is indeed essential, sooner or later, to the prosperity of every well-ordered park."
Mr. Meynell's famous foxhounds have been adduced, as showing that no ill effects follow from close interbreeding; and Sir J. Sebright ascertained from him that he frequently bred from father and daughter, mother and son, and sometimes even from brothers and sisters. With greyhounds also there has been much close interbreeding, but the best breeders agree that it may be carried too far. (17/17. Stonehenge 'The Dog' 1867 pages 175-188.) But Sir J. Sebright declares (17/18. 'The Art of Improving the Breed' etc. page 13. With respect to Scotch deerhounds see Scrope 'Art of Deer Stalking' pages 350-353.), that by breeding in-and-in, by which he means matching brothers and sisters, he has actually seen the offspring of strong spaniels degenerate into weak and diminutive lapdogs.