Horses in warfare of today's English saddle. Both the Scythians and Assyrians used pads with added felt attached with a surcingle or girth around the horse's barrel for increased security and comfort. Xenophon mentioned the use of a padded cloth on cavalry mounts as early as the 4th century BC. The saddle with a solid framework, or "tree", provided a bearing surface to protect the horse from the weight of the rider, but was not widespread until the 2nd century AD. However, it made a critical difference, as horses could carry more weight when distributed across a solid saddle tree. A solid tree,
Animal testing on frogs which reaches its reproductive age in five months rather than one to two years (as in "X. laevis"), facilitating faster studies across generations. The genome sequence of "X. tropicalis" was scheduled to be completed by 2015 at the latest. Frogs are widely used in classroom dissections and teaching exercises. Animal testing on frogs Frogs have been used in animal tests throughout the history of biomedical science. Eighteenth-century biologist Luigi Galvani discovered the link between electricity and the nervous system through studying frogs. The African clawed frog or platanna, "Xenopus laevis", was first widely used in laboratories in pregnancy assays in