672 



Regeneration 



A mutual inhibition of regeneration is ob- 

 tained when many stems or stolons are 

 present as compared with few. Widely sep- 

 arated parts regenerate better than crowded 

 parts. This phenomenon is best explained 

 as a more rapid accumulation of inhibitory 

 substances by many as compared with few 

 regenerates. The optimum number will de- 

 pend on temperature and rate of circulation 

 of sea water and on proximity of regener- 

 ates as discussed above. 



Gaseous exchange. It is seen from the fore- 

 going that temperature, circulation and pop- 

 ulation density are related to gaseous 

 exchange and excretions. Oxygen stimulates 

 regeneration in Tubularia and carbon diox- 

 ide inhibits it (Goldin, '42). Increasing 

 hydrogen-ion concentration also inhibits. In 

 ascidians, carbon dioxide, urea and uric acid 

 inhibit. The inhibitory effect on regeneration 

 in Tubularia of accvimulated carbon dioxide 

 at high population densities is shown by 

 the use of Warburg manometers. With large 

 numbers of stems of Tubularia in the War- 

 burg flasks and no potassium hydroxide to 

 absorb carbon dioxide, no regeneration 

 occurs. The same number of stems in a flask 

 with potassium hydroxide regenerate com- 

 pletely. Since the respiratory quotient dur- 

 ing regeneration is 1.0 it may be that carbon 

 dioxide and ammonia are the chief excretory 

 products. 



Salt balance. Calcium salts are particularly 

 necessary for cell aggregation of the disso- 

 ciated cells of the sponge (Galtsoff, '25). In 

 absence of the Ca** ion, dissociated cells do 

 not aggregate and therefore no regeneration 

 is possible. Ca** no doubt acts on the cell 

 surface to maintain the intercelUilar matrix 

 as it does in the dividing egg. 



Amino acids. The specific quantitative and 

 qualitative effects of various amino acids 

 have been investigated for a number of 

 years by Hammett ('43) and his co-workers 

 on regeneration of hydroids and growth of 

 other forms. ITie process of regeneration is 

 broken up into a number of individual 

 processes and the papers of this school should 

 be consulted for details. 



Radiations often inhibit regeneration with- 

 out interfering with maintenance of life. 



METABOLISM AND REGENERATION 



Here is an attractive new field for investi- 

 gation. The ultramicrochemical and ultra- 

 micromanometric methods of the Linder- 

 str0m-Lang and Heinz Holter school plus 

 the methods of Kirk and his co-workers 



have made possible exact studies on masses 

 of tissue of the order of magnitude provided 

 by regenerates. The cytochemical methods 

 for phosphatases and nucleoproteins offer 

 the opportunity for studying phosphate trans- 

 fer and the role of nucleic acid during re- 

 generation. Some progress has been made 

 and has been reviewed by Brachet ('50). 



The analysis of the problem appears to 

 be as follows: Energy is required for the 

 differentiation of cells. The initial source 

 of this energy comes from cellular oxida- 

 tions. The free energy of cellular oxidations 

 is transferred and conserved in an energy- 

 rich phosphate bond. Compounds containing 

 the energy-rich phosphate bond transfer 

 phosphate to proteins and the free energy of 

 the splitting of an energy-rich bond is uti- 

 lized in performing work. The work may 

 be lifting a weight, as in mviscvilar contrac- 

 tion, or the work may consist in change in 

 cell shape and the chemical constitution of 

 the cell. In this analysis the critical linkage 

 between the oxidations and the performance 

 of work appears to be through phosphate 

 compounds and the controlling factors may 

 be the enzymes which split and transfer 

 phosphate. 



In this connection Jaeger and Barth ('48) 

 have shown that the undifferentiated stolon 

 cells of ascidians have no water-extractable 

 apyrases while the zooids do. As the stolon 

 differentiates into a zooid the apyrases ap- 

 pear. The initial step in any differentiation 

 may be the formation of a new apyrase 

 which transfers the energy of oxidations to 

 the specific work required for the formation 

 of a specific cell type. 



REFERENCES 



Barth, L. G. 1938 Quantitative studies of the 

 factors governing the rate of regeneration in 

 Tubularia. Biol. Bull., 7-^.155-177. 



1940 The process of regeneration in 



hydroids. Biol. Rev., /5.-405-20. 



, and Barth, Lucena J. 1950 The control 



of differentiation by external factors. Anat. Rec, 

 108:Sm. 



Berrill, N. J. 1951 Regeneration and budding in 

 tunicates. Biol. Rev., 2^.-456-475. 



, and Cohen, A. 1936 Regeneration in 



Clavellina lepadiformis. J. Exp. Biol., /3.-352- 

 362. 



Brachet, J. 1950 Chemical Embryology. Inter- 

 science Publishers, New York. 



Child, C. M. 1929 Lateral grafts and incisions as 

 organizers in the hydroid Corymorpha. Physiol. 

 Zool., 2-342. 



1942 Patterns and Problems of Develop- 

 ment. University of Chicago Press, Chicago. 



