The effects of infused materials upon the regeneration of newt limbs: I. Blastemal extracts in denervated limb stumps

Denervated and amputated newt limbs are usually unable to regenerate. When such limbs were infused with extracts from limb blastemata, however, they were able to form a blastema and thus begin the process of regeneration. After the initial establishment of a blastema, limbs rarely continued to grow and either retained the growth as a static enlargement or lost it by resorption. One limb among the many tested seemed to form a complete regenerate in the absence of nerves. At the least, however, the normal response of amputated limbs to denervation was altered and new growth began. Even when infused limbs did not regenerate as an immediate response to the infusions, they frequently began to grow several weeks later. This belated growth activity was evidently supported by a renewed supply of nerves but probably would not have occurred without the earlier infusion treatments. As a rule, denervation renders an amputated newt limb permanently nonregenerating unless the limb tip is reamputated once the nerves have regenerated. Different fractions of blastemal extracts produced different frequencies of response. The most effective fraction was prepared to contain the bulk of cellular ribonucleoproteins. After infusion with this fraction, limbs produced an early blastema in 79% of the cases. The fraction containing cellular particulate matter produced early blastemata in 44% of limbs infused. Limbs infused with buffered saline solution showed similar responses in only 11% of the cases. Since blastemata began to develop on denervated limbs infused with blastemal extracts, it appears that the extracts were able to substitute in some degree for the trophic factor that would normally have come from nerves. The fact that complete limb regeneration rarely followed the formation of blastemata suggests that nerves normally bring about regeneration by some factor which the blastemal extracts did not supply.