Close in-breeding without the infusion of new blood is probably the cause of the decrease in their numbers at the present day, specimens being more difficult to procure and fetching much higher prices than they did formerly, at least in England and in France.
The Hussite wars, the feuds of Burgundian and Armagnac, the renewal of the Hundred Years' War, all prevented it from drawing new blood from the west.
In Palestine, on the other hand, the downfall of the old monarchies and the infusion of new blood gave fresh life to the land.
A constant immigration from the West, bringing new blood and recruiting the stock, could alone have maintained its vigour; and such immigration never came.
It is not impossible to combine these views, and place the seat of power still in Crete, but ascribe the Renascence there to an influx of new blood from the north, large enough to instil fresh vigour, but too small to change the civilization in its essential character.
Troublesome insects, vampire bats, and the failure to introduce new blood into the degenerated herds, are responsible for its decline.
There was thus a steady immigration into the kingdom, to strengthen its armies and recruit with new blood the vigour of its inhabitants.
When this process has reached a certain stage and all the absorption necessary has occurred the new blood vessels, from the increasing pressure of the successive fibrous layers, gradually dwindle and become obliterated, i.e.