Siddha medicine A system of medicine practised in Tamil areas of Southeast India and by Tamil-speaking people elsewhere. The system is based on humoral concepts of wind, bile and phlegm and on diagnosis by the analysis of the pulse and the appearance of the urine. The darker the urine, the more severe the disease. It includes yogic practices, faith in the miraculous alchemical properties of mercury and sulphur, and the prolongation of life through rejuvenating treatments especially the regulation of the breathing. It is believed that eternal youth is to be achieved by 21,600 respirations a day.