This essay provides information about the Regeneration!

Regeneration is an excellent ability of the adult tissue to repair any damage done to the body by autotomy i.e., voluntary separation of a part of the body, and accidental injury in nature or imposed by man under experimental conditions. This may involve replacement of dead or damaged cells, healing of a wound, replacement of lost part or the regeneration of the whole organism from a piece of body. It reflects the reawakening of the developmental processes of morphogenesis and differentiation in the adult, when such processes normally cease in post-embryonic life of the organism.

This ability is almost present throughout the animal kingdom. Hence “the ability of an animal or organism to repair a wound, which partially destroys tissues of the animal’s body or the damage involving the loss of an organ or larger part of the body which may be renewed, is thus called the process of regeneration.” Trembley first discovered it in Hydra in 1740. Of all the animals, coelenterates possess the greatest ability of regeneration, being highest in the polyploidy.

It is common in planarians, nemertean and annelids, but poor in mollusks, nematodes, arthropods and echinoderms. Among vertebrates, it is remarkable in urodeles, but limited in anurans, fishes and lizards and very poor in birds and mammals.


In a healthy normal adult animal, many kinds of cells need replacement after a species -specific span of time. For example, there are approximately 25 × 1012 red blood cells in the active circulation of the human adult at any time.

About one percent of these cells are replaced daily; all the red blood cells are replaced every four months. Such replacement processes are also common in skin cells, cells in the lining of the uterus, and cells in the lining of the gastro-intestinal tract, and thus on the cellular level, it is a state of dynamic equilibrium.

This morphological expression of the functional activity of living organs may be called as physiological regeneration. Other animals are able to reform a part of body that is removed, just as the embryo is able to replace lost parts.

For example, the regeneration of limb in salamander or lost part of tail in a lizard. This is known as reparative regeneration and bears great similarity to the processes and events of embryonic development. Some animals in their adult stage retain much of the labile organization of the early embryo and are able to form two or more adults from a single adult, as in Hydra, each part of bisected organism will develop into a full fledged adult.


Aristotle recorded the process of regeneration in his De generation animalum written over two hundred years ago. Trembley (1740) first discovered the regeneration process in Hydra. Galtsoff (1925) studied the process in sponges as reconstitution phenomenon in which if cells of the sponge are disaggregated, the isolated cells can aggregate and reconstitute a new sponge body.

According to Gierer (1974) it is possible to achieve reconstitution in case of Hydra also. This phenomenon is fascinating to man even today and recent studies on this process are made by Berrill, Schmidt, Burnett, Thornton and many other workers.