If the game freezes, just click inside it (games can get unresponsive if you click elsewhere on the page).
You have discovered a new formula that will cure the zombies and transform them into humans. But you still need some time to perfectionise the serum! Pour the milk, syrups and the anti-virus serum when the meter is centered and give your super humaniser blend to the waiting zombies. Buy upgrades at the end of each day and unlock new zombies as you try to survive, and see how many zombies you can cure!