 The city of Fustat also had multi-storey tenement buildings (with up to six floors) with flush toilets, which were connected to a water supply system, and flues on each floor carrying waste to underground channels.A basic form of contagion theory dates back to medicine in the medieval Islamic world, where it was proposed by Persian physician Ibn Sina (also known as Avicenna) in "The Canon of Medicine" (1025), the most authoritative medical textbook of the Middle Ages.He mentioned that people can transmit disease to others by breath, noted contagion with tuberculosis, and discussed the transmission of disease through water and dirt.