Jockey Michael Martinez, whose spinal cord was severed in a horrific racing spill Sunday at Golden Gate Fields, could be a candidate for implantation of embryonic stem cells in hopes of mending the spinal cord.\r\nThe 24-year-old rider&rsquo;s life hung in the balance Monday when bleeding in his brain began at a high rate before being stabilized by Monday afternoon. His condition at Highland Hospital in Oakland, Calif., remained critical but stable on Tuesday.\r\nAfter a restful night under sedation Monday, Martinez showed improvement Tuesday when his lung function improved enough for him to be removed from a breathing machine and a chest tube was removed from his right side.\r\nThe 24-year-old rider spoke for the first time since the accident, answering &ldquo;Michael&rdquo; when asked his name. He also asked his wife, Charlotte, if he could be released from the hospital.\r\nThe injury, which has left Martinez paralyzed from the waist down, was &ldquo;one of the most devastating injuries we&rsquo;ve seen,&rdquo; said Golden Gate Fields&rsquo;s track physician, Dr. David Seftel.\r\nAn 11-hour operation Sunday night by Dr. Frederico Castro-Moure, Highland&rsquo;s chief of neurosurgery, removed shards of fractured vertebrae from Martinez&rsquo;s spinal cord, which was cut completely. Rods were then attached to stabilize his spine.\r\nTesting of embryonic stem cells in animals has shown the cells can help to regenerate severed spinal cords. Because of his age, good physical condition and small frame, Martinez would be a perfect candidate, said Seftel.\r\nAfter swelling in the spinal cord recedes, doctors will determine if the cord can be reattached without putting tension on it. If it can be reattached, stem cells would be implanted on both sides of the spinal cord in hopes they would mend the cord together.\r\nMartinez was injured when favored Fair &rsquo;n Warmer apparently clipped heels while in tight near the three-eighths pole of a $4,000 claiming race at five furlongs. Films did not provide a clear view of the incident, and a stewards&rsquo; inquiry could not place blame for the incident.\r\n&ldquo;The spinal cord was transected upon impact, then the horse rolled over on him, fracturing the vertebrae,&rdquo; said Seftel. &ldquo;But he&rsquo;s an incredible fighter, and when we got to him, he displayed incredible strength and will power and was breathing on his own.&rdquo;\r\nMartinez&rsquo;s agent, Dennis Patterson, and Fair &rsquo;n Warmer&rsquo;s trainer, Billy Morey, went to Highland Hospital after the accident and were told early X-rays indicated a concussion and fracture. Morey drove Patterson back to the track to get his car. Patterson returned to the hospital and only then was advised of the severity of Martinez&rsquo;s injuries.\r\n&ldquo;It was totally different from when we left the track,&rdquo; said Patterson.\r\nMartinez&rsquo;s wife, Charlotte, the daughter of jockey Julio Garcia and due to deliver the couple&rsquo;s first child later this month, and Martinez&rsquo;s cousin jockey Alex Solis are with Martinez.