V METABOLIC CHANGES 621 



water facilitates the movements of cells in defence and demolition (Onweleen, 

 191 7) and in blastema-formation. It probably also facilitates proteolysis, for the 

 amount of hexosamine liberated from mucoproteinsis proportional to the hydration 

 of the tissue (Boas and Foley, 1954). Intracellularly it restores a more youthful 

 condition necessary for growth and proliferation. 



Dilution of the external medium does increase the water-intake of aquatic 

 animals, and it accelerates regeneration in brackish water Planarians (Lloyd, 

 1919; Steinmann, 1932) and in the marine Coelenterates, Pennaria (Keil, 1932) 

 and Tiibularia (Loeb, 1892). Reciprocally an hypertonic medium depresses regen- 

 eration-rate (Morgulis, 1909), particularly in fresh, water animals (Sayles, 1934; 

 Davenport, 1 899) . Dilute alcohol increases tissue hydration and promotes regenera- 

 tion whereas concentrated alcohol dehydrates, and retards regeneration (Mor- 

 gulis, 1909; Bilski, 1926). 



In the polychaete worm, Podarke (Morgulis, 1909) and in the brine shrimp Artemia 

 (Sciacchitano, 1925), accustomed to high salinities, regeneration is retarded by dilution of 

 the medium. Concentrated salt-solutions, applied for a short time to the amputation-sur- 

 face of the limbs of adult Anura, which normally show only very abortive regeneration, 

 greatly improves the process (Rose, 1942, 1944; Polezhayev, 1946) but this is a very differ- 

 ent phenomenon, — the result of damage by the concentrated salt. Saline improves the 

 regenerativepower of posterior pieces of planaria (Watanabe, 1941), again possibly through 

 depressive action, — differentially on the anterior part of the parent body. 



Lessona {cf. Morgan, 1901, p. 93) found that terrestrial salamanders regenerate limbs 

 more slowly than aquatic types, and adult Anura, which regenerate very poorly compared 

 with adult Urodeles, in general are more terrestrial than the latter. A number of groups 

 with poor powers of regeneration are terrestrial: insects, reptiles, birds and mammals. It 

 might be concluded, therefore, that terrestrial conditions are inimical, owing to relative 

 desiccation. However Goodwin (1946) found no significant difference in regenerative 

 power between Urodeles of the same species regenerating in air and in water. Many ter- 

 restrial animals in fact regenerate well, not only moist-skinned types such as terricolan 

 Turbellaria and earthworms but also insect-nymps, woodlice and centipedes. The terres- 

 trial, pulmonale snails regenerate their shells much more rapidly than do the marine 

 gastropods (Waage and Mittler, 1953). Even the mammals heal their skin very well and 

 they regenerate the internal organs as rapidly as in any group. Any apparent correlation 

 of poor regenerative power with the terrestrial habitat may be in fact a correlation with 

 large body-size, with tissue-differentiation, which itself usually involves tissue-dehy- 

 dration, or with determinate growth. 



The movement of water into the cells, locally, during the R-phase is associated 

 with an ingress of sodium and egress of potassium (Anon., 1951). Tissues in general 

 lose K and take in Na also after removal from the body to culture medium 

 (Davies, 1954). The trend is reversed when the cells begin to proliferate. The ini- 

 tial movements are favoured by anaerobic and the restoration by aerobic condi- 

 tions, so that the latter are inhibited by respiratory poisons, and particularly those 

 which uncouple phosphorylation from oxidation. Glutamic acid and its derivatives 

 prevent the initial K-loss; these ion-movements therefore are associated with 

 fundamental components of metabolism. The resemblance between the whole 

 sequence and that in nerve-conduction needs no further emphasis (p. 643). 

 Cholinesterase affects the movements across the wall of other cells in the same 

 way as across the nerve cell-membrane (Danielli, 1954). 



Lilerature p. 64g 



