By 3,500 ., city-states had emerged in southern Mesopotamia. These Sumerian city-states included Ur, which according to the Bible was the birthplace of Abraham. The city of Babylon became the capital of much of the area under King Hammurabi (1,792-1,750 .), who is famous for the collection of laws known as the Code of Hammurabi. The northern part of the country, known as Assyria, rose to prominence during the first half of the first millennium (900-630 .). King Nebuchadnezzar II (604-562 .) undertook vast building projects at Babylon that brought it to the height of its splendor. Babylon fell to the Persians in 539 . The Persians were, in turn, conquered by the Greeks, led by Alexander the Great, in 331 .
In the 17th century people knew the principle of the concave and convex lenses . Eyeglasses can be produced with single lenses that correct for distance vision or up close, or they can be manufactured with multifocal lenses, which correct both distance and reading. Concave glass is used to correct nearsightedness, so that the rays of light are diverged. Convex lenses are used to aid the correction of farsightedness, so that the light rays are converged. Cylindrical lenses used to correct astigmatism were invented by Sir George Airy in 1825. Bifocal lenses can be used to treat with nearsightedness and presbyopia (with a lower part for viewing objects near at hand (as in reading)). They were the first devised by Benjamin Franklin in 1784.
The researchers confirmed the hypothesis by presenting a wild-caught rat with branches and roots of the Acokanthera tree. The rodent proceeded to gnaw and masticate the bark (avoiding the leaves and fruit) and apply the "slaver" on its flanks. Further, the research team employed electron microscopes to examine the unique structure of the flank hairs. In doing so, they found that the perforated cylindrical structure of the hairs facilitates the rapid absorption of the poisonous saliva. Interestingly, ouabain has also been used by doctors for centuries as a clinical treatment against congestive heart failure.