Just as John comes into the hallway, the shift-changes. The hall fills with hundreds of Delta twins who line up when an Alpha calls out that it is soma distribution time. John is suddenly overwhelmed with anger, and thinks that soma caused Linda's death. He shouts that soma is poison, and tells the Deltas to throw it away. Just the idea terrifies and angers the Deltas.
John is threatening the very bedrock of World State society. Soma is what ensures happiness, and therefore gives the State its power over its people. John is trying to save the Deltas from a slavery they love.
Bernard and Helmholtz get a phone call telling them what the Savage is doing. They hurry to the hospital. They arrive just as the Savage starts dropping soma out the window, causing the Deltas to riot. Helmholtz shouts "Men at last!" and runs to help the Savage. The two fight off the Deltas and throw more soma out the window.
Helmholtz's cry "Men at last!" shows his realization that by conditioning his emotions and guaranteeing his happiness, his culture has made an infant. Now he stands up for what he believes, takes responsibility for himself, and acts like an adult.
When the police arrive, they spray soma vapor into the air to quiet the Deltas. The police take Helmholtz and the Savage into custody. Bernard tries to slip away, but the police take him too.
That soma is sprayed into the air to quiet mobs further illustrates the drug's primary purpose of keeping the masses happy and society stable.