622 REGENERATION AND GROWTH 7 



[h) Inorganic cations 



A correct balance of the physiologically important inorganic cations therefore 

 is essential for normal regeneration (Davenport, 1899; Morgulis, 1909; Loeb, 

 i924;Korschelt, 1927; Beadle and Booth, 1938; Von Bertalanflfy and Rella, 1941). 

 Any serious disturbance of the balance retards regeneration and causes qualitative 

 abnormalities. Regeneration is accelerated also by the supplement of an inorganic 

 element such as phosphorus, available in limited concentration (Needham, 1947b). 



Calcium, like phosphorus, has a further function, as skeletal material in inter- 

 cellular cement (Chambers, 1942), in bone (Murray, 1936; Roche and Morgue, 

 1939; Bohr and Sorensen, 1950; Imanaga et al., 1952; Schotte and Lamy, 1953) 

 and in the exoskeleton of molluscs and arthropods. Calcium is relatively easily 

 demonstrated in situ, and estimated accurately, and its movements during regener- 

 ation are becoming well-known. An R-phase of mobilisation (Roche and Mor- 

 gue, 1939) is followed by a P-phase of synthesis of insoluble calcium compounds. 

 Mobilisation is most rapid locally at the site of fracture of a bone (Schotte and 

 Lamy, 1953) and grades away fairly sharply, little coming from other bones 

 (Bohr and Sorensen, 1950). However some is supplied systemically and there is 

 an increased rate of exchange of Ca between plasma and bone (Bohr and Sorensen, 

 1950). Injected Ca is taken up mainly by the regenerating bone but any excess is 

 stored in the liver and kidney (Imanaga et al., 1952). The normally growing 

 epiphyses also take up a large amount, by contrast with intact parts of the diaphy- 

 sis. In the regenerating limb of Triturus calcium increases almost from the outset 

 and reaches maximal concentration by the tenth day, returning to normal at the 

 end of regeneration, around the thirty-fifth day (Schotte and Lamy, 1953). In 

 the fractured limb-bone of the rat the maximal content, about three times normal, 

 is reached at the end of the second week (Imanaga et al., 1952). 



VI. THE EFFECT OF EXTRINSIC FACTORS ON REGENERATIVE GROWTH 



Most physical and chemicals agents which affect regeneration directly have the 

 same action as on normal growth. Frequently, however, an external agent acts 

 indirectly, triggering off a response appropriate to, and often counteracting the 

 direct effect of, an external situation of which this agent is the most infallible sig- 

 nal. For instance, light acts as a trigger for the regeneration of the hydroids Euden- 

 drium (Loeb, 1896; Goldfarb, 1906), Tubularia and Pennaria (Peebles, 1899) and 

 Syncoryne (Nakamura, 1941); probably it is a signal of abundant food in the ulti- 

 mate form of photosynthesising microorganisms. In other animals, by contrast 

 (Marcus, 1926; Coe, 1929), and even in some other hydroids (Torrey and Mar- 

 tin, 1 910) light inhibits regeneration. In Sabella it inhibits the epimorphic compo- 

 nent only, of regeneration. In the limbs of Carcinus the inhibitory action is in- 

 direct, via the sinus gland. However visible light reduces the direct inhibitory effect 

 of shorter wave-radiations (Giese, 1950). Light is surprisingly irrelevant to the 

 regeneration of the eye of Crustacea (Korschelt, 1927; p. 202) and of the lens 

 of the urodele-eye (Riibsaamen, 1950), for the ultimate function of which it is 

 indispensable. 



