Another good reason for researchers to better understand the biochemical roots of regeneration in lower animals such as newts and salamanders: "Goro Eguchi has shown that a newt's healing powers don't diminish with age. As long as they live, they retain the ability to efficiently regrow their body parts (or at least, the lenses of their eyes), even if they have to do so over and over again. We've known about the abilities of newts and other salamanders for over 200 years, thanks initially to Lazzarro Spallanzini, an Italian biologist and Catholic priest. But the limits of this ability have been unclear. Spallanzani once amputated limbs from a salamander six times over three months, and watched them grow back. ... The salamanders could repeatedly regrow their limbs, but eventually, abnormalities crept in. For example, the animals would occasionally develop missing bone structures. Both Spallanzani and Bonnet (and, indeed, Charles Darwin after them) held that newts regenerate their body parts less efficiently as they get older, especially if they accrue repeated injuries. But Eguchi thinks that these experiments, while historically important, were also flawed. The exposed stumps of the severed legs would have been exposed to the messy environment, which might have scuppered a clean regeneration. To truly test the extent of these animals' powers, Eguchi set up a 16-year-long experiment. In 1994, he collected several Japanese fire-bellied newts (Cynops pyrrhogaster) and successfully kept them in captivity. During that time, Eguchi periodically anaesthetised the animals and carefully removed the lens from their eyes. The surgeries involve a small nick to the cornea that quickly sealed, creating a protected environment where the lens could regenerate without any influence from the outside world. This happened 18 times in total. Eguchi found that the 17th and 18th lenses were exactly the same as the original ones, and those from untouched newts of the same age."

Link: http://blogs.discovermagazine.com/notrocketscience/2011/07/12/newt-healing-factors-unaffected-by-age-and-injury/