Scrive clicked the new cartridge into place in his forearm and felt the cold rush snaking from his arm to burst somewhere inside his head. 
Next he checked the small plexi inspection window where his blood was already changing from a bright red back to orange. He knew that within another twenty minutes it would again be the safe yellow colour.
Like everyone, he knew that red blood spelt danger and he had been particularly careless to let his system deplete its supply of the tropus for so long. 
He could now feel a pulse and almost a bubbling sensation on the left side of his head above the eye-line. He  knew this was his body regaining its equilibrium. He squeezed both his hands into a fist shape they way they were taught and used his two middle fingers to massage the fleshy areas below his thumbs whilst his system adjusted.
Another five minutes and he was walking to the Tube station. He lived less than ten minutes on foot from the nearest stop and his ride to today’s meeting was around fifteen minutes. He could feel the cartridge working and his relaxed acceptance of the day’s tasks was already returning. 
He looked briefly towards the sky. A jagged spark had flicked across moments before and now there were gentle vapour trails crawling behind a tear along the route of the River Thames.