Abstract
Naturally occurring hemorrhagic and thrombotic diseases of animals closely parallel their human counterparts. While such models may be particularly useful in studying the pathogenesis of human disease, it is usually more realistic to depend upon experimentally induced disease models. The species selected for use is therefore of major importance in providing meaningful extrapolation to humans, as are the experimental design and type of procedure (in vitro, ex vivo, in vivo). Regardless of the test system used when in vitro procedures are employed, these must be translated eventually to the in vivo situation. Information about the normal aging process of different species is important here and should influence selection of the species and test system. The ideal situation may not be feasible or pertain because of cost, availability, size, and investigator familiarity, or lack thereof, with the most suitable species or model.