The control of tuberculosis: a continuous game of snakes and ladders

'The traditional Indian game of snakes and ladders is played by rolling dice to determine how many squares a player can move his marker up the board, starting at square one and finishing at square one hundred... [there is] an austere geometry of squares broken by angled ladders and snakes with yawning jaws. Landing at the foot of the ladder meant you could climb it, sometimes moving thirty squares in a single throw. You could also make it to square ninety nine, only to encounter a snake.... Then you had to slide down the serpent'.