The Oldie: Profitable Wonders – March 2011
Regeneration
The salamander is a most intriguing creature, its poetic sounding name being derived from the Persian for ‘the fire within’—as, according to the 12th century Latin text The Book of Beasts,’it prevails against fire … the only creature that can live in a blaze without being hurt’. This charming notion, it is suggested, derives from the effect of adding its favoured habitat of damp logs to a fire—from which it must be presumed it was sometimes observed to escape unscathed.
There are around 500 species of this splendid amphibian ranging in size from the minute at just over an inch long to the six foot Chinese Giant Salamander. The most familiar, and a popular family pet, is the handsome (if redundantly named) Fire Salamander whose shiny black skin is splashed with what looks like splodges of bright yellow paint.
They are for the most part carnivorous feeding on insects, snails and slugs. The Palm Salamander from Central America possesses reputedly the fastest moving tongue in the animal kingdom whose explosive thrust and elasticated recoil captures its prey on its sticky padded tip in less than a thousandth of a second—far too rapid to be seen by the human eye.
But the most impressive attribute of the salamander, for which it is justly famous, is its extraordinary ability to regenerate injured or amputated limbs as first described in 1769 by the Italian biologist (and catholic priest) Lazzaro Spallanzani.
Within a few hours cells start to migrate from the cut surface of the limb stump to cover the wound beneath which a ‘blasteme’ of tissue is transformed into the bone, nerves, muscle and blood vessels that’pushes out’ to form a perfect replica of the missing appendage.
This process is similar to the formation of the limb bud during early embryonic development but with the remarkable feature that the new limb exactly replicates the missing part. Thus, an amputation at the level of the ankle will result in regeneration of foot and toes, whereas at the hip the leg will regrow in its entirety. Remarkably too, the blasteme is also autonomous containing within itself all the necessary instructions for the regenerative process independent of any influence from the amputated stump—so will regrow the limb even if transplanted to some other site, such as the eye.
Spallanzani’s observations prompted biologists to seek out similar more or less extraordinary instances of regeneration: insects such as the locust and cockroach can also, like the salamander, regrow lost limbs, as can the crab and lobster; cut the eye bearing stalk of a snail and it will grow another, and repeatedly so if the experiment is repeated; the star fish exhibits ‘bidirectional regeneration’, replacing an arm if lost while the ‘lost arm’ in turn will give rise to a new star fish; lizards will regrow a tail surrendered to a predator, and the stork and chicken can regenerate a damaged beak.
The planarian worm most impressively of all will, if chopped into 250 pieces, regrow a head and tail for each. They will, in the interim, feed off their own tissues to provide the energy necessary to survive before regrowing a new mouth and gut.
We might rightly admire such exuberant examples of the normal processes of healing and repair that, observes Alejandro Alvarado of the Carnegie Institution in Washington,’has withstood the probing of scientific inquiry for 250 years and still awaits a satisfactory mechanistic explanation’. Perhaps the more instructive aspect of the phenomenon of regeneration is its insight into how organisms possess a wholeness of form that transcends the materiality of their constituent parts. Those parts can be destroyed yet the salamander and star fish, crab and planarian worm can still reconstitute that wholeness—as if guided by some metaphysical intuition of what is entailed in existing in their entirety.