684 



Regeneration 



the blastema and weaker at the base of the 

 limb. This brief increase in level extends 

 over the fifth and ninth days, after which 

 there is a decrease, and no alkaline phospha- 

 tase is demonstrable after the twelfth day. 

 As is apparent in Figure 240, changes in 

 the phosphatase level occur with or before 

 the first histological criteria of differentiation. 



It is essentially a formation from mesen- 

 chyme derived from fibroblast cells rich in 

 alkaline phosphatase or by similar cells 

 secured from dedifferentiation of muscle and 

 cartilage. 



The possibility of an epidermal contribu- 

 tion to the blastema seems at present most 

 unlikely on the basis of former histological 



> '>■ 



> 



Fig. 240. 



both in embryonic limb formation and in 

 larval limb regeneration. The cells compos- 

 ing the regeneration blastema react dis- 

 tinctively to phosphatase stains. Fibroblast 

 and dedifferentiating muscle appear to fur- 

 nish the chief components contributing to 

 the blastema, a finding in agreement with 

 those of Butler (33), Thornton ('38a,b, '42) 

 and Forsyth ('46). The contribution of the 

 epidermis to the blastema, as advanced by 

 Godlewski ('28) and Rose ('48), receives 

 no support from the studies on phosphatase 

 localization and level. The phosphatase in 

 the epidermis appears after the preliminary 

 phases of regeneration are complete and it 

 is seldom that the epidermis elements merge 

 with the blastema. 



The problem of blastema origin then 

 stands at present on a fairly substantial 

 accumulation of material which clearly 

 supports the older histological observations. 



studies which show the non-participation of 

 epidermal structures as well as the later 

 studies of Thornton ('38a,b), Manner ('53), 

 Heath ('53) and Karczmar and Berg ('51). 

 The descriptions of careful observers cannot 

 easily be thrown aside and the indirect 

 evidence on mitotic loci and the abundance 

 of embryonal fibroblasts, combined with 

 chimaeric limb regeneration studies and the 

 alkaline phosphatase correlation, all add to 

 the fund of knowledge which places the 

 burden of proof upon those who claim an 

 epidermal contribution to the blastema. On 

 the basis of the evidence, it is much more 

 likely that the epidermis is either passive or 

 an inhibitor of regeneration. 



This idea is supported by Rose's ('44, '45) 

 observations on regeneration of the limb in 

 adult anurans. These forms are recalcitrant 

 to limb regeneration, but limb development 

 can be initiated by preventing wound heal- 



