Editor's note: This story contains graphic details of amputee accidents that may be distressing to some readers.
TAPACHULA, Mexico (CNN) -- In the first four months of this year, more than 20,000 illegal migrants boarded the "train of death" at the railhead in Arriaga, southern Mexico, according to diplomats in the region. They all had one aim: "El Norte", the United States.
There are no official figures of how many may have fallen from the train and been maimed or killed after falling under its wheels.
But Olga Sanchez, who has been running a hostel to care for mutilated migrants in the city of Tapachula, says that over the past 20 years she has tended to thousands of men and women who have lost legs and arms.
Mexican Ruben Perez, 28, worked in construction and farming until he set out to cross illegally into the U.S. two years ago. He fell off the train near the Mexico-U.S. border and lost both legs.
"My mom told me not to go. She said it was better to stay in Mexico even if we only had a little. But I took the decision to leave.
"I wanted to go and earn money. Most people who go are able to progress in life and save enough to build their own homes. They go and rent a room usually at first but after a year or so they have their own house. I wanted to imitate that.
"Who knows who invented the name the 'American Dream?' It's not a dream, it could have become reality for me and so that's why you have to take the risk.
"The train was going fast and I waited for it to slow up. But it just carried on so I decided I was going to grab it. I began to run but the train was quicker than me. I grabbed the ladder and hung on but then my foot slipped off and went into the wheel.
"I asked myself how I was going to get my leg out. I wanted to push with my other leg but that got sucked in too. I was clinging on and my leg was spinning around in the wheel until it finally spat me out and I was crying for help. I was afraid to let go because I had no legs.
"Eventually I let go of the train and because I had no legs I just rolled. I shouted for help then passed out.
"I felt like a dog. One of those dogs that's dying in the street and is worth nothing. I thought to myself now I'm worth nothing."
Marcos Castro, 19, worked in construction before he left Honduras. He lost his right leg in April this year as he slipped under the train in southern Mexico, close to the border with Guatemala.
"I was hanging to the train but my sneakers slipped and the train was moving fast. I hung on but was only hanging by one hand and I had to let go.
"The train blows you out then sucks you in and then blows you out again. When it blew me out I managed to get my leg out but I could only get one out.
"I wanted to go to the United States to improve my life, to be able to work and to have my own things. But if I can't get there, I can't get there. What can I do about it? There's no alternative. I'll just have to go back.
"I can't continue to the United States, not anymore. How can I? My legs don't work. I'd never be able to get on that train again."
Olga Sanchez set up a hostel to care for these mutilated migrants. She says it was her promise to God after recovering from a life-threatening illness as a child.
She has received some international donations but raises the extra cash she needs to provide migrants with $2,000-a-time prosthetic legs by selling bags of home-baked bread at $2.
"Even trained medics have said to me that these migrants are dirty, worth nothing and a piece of trash. But to me the person who is dirty and has nothing is, to me, the person who is worth most. I will always defend the ones who have nothing the dirty ones, the ones left behind.
"Over the last 20 years I've seen more than 5,000 amputees. I used to pick them up from the tracks I picked up their bones and their remains, people who were almost dead.
"I remember the first one. His name was Baltazar. I picked his bones up from the track. He was dying clinging to life by a thread.
"I said to him remember you have a wife and children, remember you have to go home. Fight for your family. I was carrying his bones in my blouse. I was all bloodied.
"I laugh at the American dream. Sometimes the American dream turns into hell. It's a dream floating in the clouds. Not everybody can reach it and they suffer a tragedy."