Small steps towards understanding the greater regenerative capacity of one species: "When the spinal cord is severed in humans and other mammals, the immune system kicks in, activating specialised cells called glia to prevent bleeding into it. ... Glia are the workmen of the nervous system. The glia proliferate, forming bigger cells that span the wound site in order to prevent bleeding into it. They come in and try to sort out problems. A glial scar forms. ... However, the scar prevents axons, threadlike structures of nerve cells that carry impulses to the brain, of neighbouring nerve cells from penetrating the wound. The result is paralysis. ... The axons upstream and downstream of the lesion sites are never able to penetrate the glial scar to reform. This is a major barrier in mammalian spinal cord regeneration. In contrast, the zebra fish glia form a bridge that spans the injury site but allow the penetration of axons into it. The fish can fully regenerate its spinal cord within two months of injury. ... Scientists discovered the protein, called fibroblast growth factor (fgf), controlled the shape of the glia, and accounted for the difference in the response to spinal cord injury between humans and zebra fish. The scientists showed the protein could be manipulated in the zebra fish to speed up tissue repair even more. ... The hope is that fgf could eventually be used to promote better results in spinal cord repair in people."