Invisible but very powerful, microorganisms have always been our life companions. Alberto Angela proposes a journey to discover infinitely small creatures, showing how our life, but sometimes also our death, depends on them. The journey of "Ulisse" begins in Benin, a very poor country which like many other places on the planet represents the "front line" of the fight against microbes and viruses. And international organizations operate here which have saved many children through vaccinations. But how and when did humanity begin to use vaccines? In "Ulysses", a documentary brings to life a "revolutionary" moment: the one in which Luis Pasteur tries the impossible to save the life of a child bitten by a dog suffering from rabies. An episode that will forever change not only the lives of the people involved but also our relationship with diseases. And, today, how can we protect ourselves from infections? What precautions to use? How effective are simple gestures like washing your hands?