If I had met Zelma Lazarus, 86, last week I would not have recognised her, nor she me. Time has a way of rewriting our faces, replacing the sturdy invincibility of youth with frailty and crinkled skin. Creeping dementia had also robbed her of memories one by one till only a few important faces remained. I was not one of them.

But this shrunken woman with fading recollections whom I have called friend for 40 years had created something stunningly unexpected that will long outlive her. Of all things, it was a locomotive train that saved lives. By the time Zelma passed away six days ago, her train, the Lifeline Express, had brought new health and a better future to two million poor Indians over 217 expeditions to India’s hinterland. If you want to understand the connection between this chestnut-haired old woman and a railway train, you must first understand numbers.