680 



Regeneration 



blastema. This idea will need discussion 

 since it has been revived by Rose's ('48) 

 work. 



4. The origin of the blastema from reserve 

 cells, similar to the archeocytes of the worms 



Fig. 236. Transition from fibroblast to fibrocyte. 

 FB, Fibroblast; /, an intermediate type; FC, fibro- 

 cyte. Camera lucida drawing. X 450. (From Man- 

 ner, '53.) 



or from cells which retain their embryonal 

 capacities and potentialities. 



Unfortunately, most workers in the field 

 usually adopt an intermediate position with 

 regard to the above headings, e.g., Puckett 

 ('34) considers the blastema as a cell mass 

 composed of materials secured by complete 

 dedifferentiation of all the formed elements. 

 This logically means that the parts so gener- 

 ally derived have to undergo a complete 

 sorting-out process to attain their later def- 

 inite structural relationships. It is a com- 

 bination of like from like with an inter- 

 mediary dedifferentiation. The process of 

 this sorting out is of course very difficult to 

 follow and a causative mechanism so far 

 has not been ascertained. 



Manner ('53), like many others, has 

 studied in detail the three phases which have 

 to be considered in regeneration of the limb 

 of Tritvu-us, using as indices the changes in 

 mitotic activity of the epidermal and mes- 

 enchymal tissues during the 28 days follow- 

 ing amputation. (See Fig. 235.) 



In securing his figiires for the mitotic 

 index he has been most careful to avoid 

 some of the pitfalls of this method, e.g., 

 Litwiller ('39) has shown that the mitotic 

 index varies with the time of day; in recog- 

 nition of this. Manner has removed the 

 blastemata used for his study at a fixed time 

 for all cases. Since the epidermis is the 

 only tissue which can be counted accurately, 

 he counts the mitotic mesenchymal cells 



and compares this figure with the total 

 number of epidermal cells at any given 

 stage. A total count of all cells in the mes- 

 enchyme is practically impossible, since the 

 amoimt of debris resulting from amputation 

 is an obscuring factor which he recognizes. 

 Nevertheless, by this comparison he secures 

 a relative value which can be employed. 



Manner draws a rather sharp line in def- 

 inition between the fibroblast shown by 

 Maximow and Bloom ('52) to possess the 

 capacity for the formation of all connective 

 tissue elements and the fibrocyte which has 

 lost its embryonal capacities. 



The evidence from this paper, as well as 

 from others (Nassonov, '30; Thornton, '38b; 

 Needham, '42; Liebman, '49), all points to 

 a fibroblast cell as the effective agent in 

 blastema formation. The possible influences 

 engendered in the degeneration after am- 

 putation and the relationship of nerves and 

 muscles are taken up as logical steps in the 

 proximodistal progress of regeneration. It 

 is fairly clear that the like from like prin- 

 ciple does not hold here and that the sorting- 

 out process is conditioned by the nerve sup- 



Fig. 237. General diagram of a regenerating fore- 

 limb. M, Epidermal mitotic cell; F, mesenchymal 

 mitotic cell; n, the epidermal cells on one side, in 

 a single section, from the level of amputation to the 

 middle of the blastema. (From Manner, '53.) 



ply in the presence of muscle. Epidermis 

 certainly is not primarily needed (Weiss, 

 '27) ; bone may be climated from the stumps 

 (Weiss, '25b; Thornton, '38b), and still re- 

 generation takes place. 



Other evidence such as the regeneration 



