REGENER.\TION 99 



It is well known that the limbs of a salamander grow again 

 after they have been cut off. and we owe our accurate knowledge 

 of the regenerative processes concerned mainly to the researches 

 of Gotte* and Fraisse.f The investigations of these observers 

 show that the regeneration of the limbs and their formation in 

 embryogeny take place in a similar manner : the individual parts 

 and segments of the extremity become developed in the same 

 order, and are formed of similar cell-material in each instance. 

 Both here and in the case of the epidermis described above, the 

 regeneration is palingeneiic. 



If we take as our basis the law, which holds good at any rate 

 as regards Vertebrates, that in regeneration each specific tissue 

 can only reproduce its own specific cells, we can test the theory 

 of regeneration by taking as an example a single tissue of an 

 extremity. It is certain as regards the bones, for instance, that 

 regeneration always proceeds from the injured bone, or rather 

 from its periosteum. If the extremity is disarticulated from the 

 shoulder-girdle, for example, and the bones are uninjured, these 

 latter do not become re-formed. Although it cannot be denied 

 that the various tissues which are required for the regeneration 

 of the entire limb have an influence upon one another, especially 

 when pressure is exerted by one part on another situated near 

 to it. it is clear that the formation of new bones depends entirely 

 on the bones present in the stump of the amputated limb, which 

 not only determine the quality of the tissue, but also regulate 

 the size and shape of the bone which is to be formed anew. 

 These last-mentioned facts are the most important of all in 

 explaining the phenomenon of regeneration of a limb. From 

 what has already been said, it is evident that the bony tissue, 

 including the periosteum, can be formed from the cells of the 

 corresponding pre-existing parts. All that is necessary in order 

 that the process may take place is a supply of cells, capable of 

 proliferation, which contain 'bone-idioplasm.* and which are 

 incited to multiply by the stimulus due to the injury in the 

 tissue surrounding them. The regeneration of the epidermis 

 may be explained in a similar manner. But as regards these 

 bones, it is not merely the production of bony tissue of a definite- 



* Gotte, ' Uber Entwickelung u. Regeneration des Gliedmassen-Skeletts 

 der Molche," Leipzig, 1879. 

 t Fraisse, loc. cit. on p. 97. 



