Cupping developed over time from the original use of hollowed animal horns to drain toxins out of snakebites and skin lesions. Horns evolved into bamboo cups, which were eventually replaced by glass. Therapeutic applications evolved with the refinement of the cup itself, and with the cultures that employed cupping as a health care technique. The true origin of cupping therapy remains in obscurity. The Chinese expanded the utilization to include use in surgery to divert blood flow from the surgery site. Cupping eventually developed into a separate therapy, with healers treating a variety of conditions. Early written records date from 28 AD, and a traditional Chinese saying indicates "acupuncture and cupping, more than half the ills cured". Chinese medicine observes that cupping dispels stagnation of Blood and Chi, along with external pathogenic factors that invade a weakened constitution. A depleted constitution is often a result of depleted "Jing Chi", or original essence. This will usually progress to a weakened "Wei Chi", or defense (immune system). The Egyptians produced a text on ancient medicine that discussed the use of cupping for conditions such as fever, pain, vertigo, menstruation imbalances, weakened appetite and accelerating the "healing crisis" of disease. From the Egyptians, cupping was introduced to the Greeks and eventually spread to ancient cultures in many countries of Europe and even the Americas. In recent history, European and American doctors widely used cupping in practice into the late 1800's. Research papers were written in the 19th century, and a collaborative effort between the former Soviet Union and China confirmed the clinical efficacy of cupping therapy. It became an official therapy to be found in all Chinese hospitals. New cupping sets were introduced using pumps to create the vacuum, and these sets were carried by medical supply companies well into the 1940's.