6l4 REGENERATION AND GROWTH 7 



proliferating micro-organisms (Jeener, 1952). This is good evidence that it is 

 directly involved in the synthesis of cytoplasmic proteins. DNA may catalyse the 

 synthesis of proteins of the nucleus (Allfrey et al., 1955) but these are a small 

 fraction of the total protein. Indirectly DNA is required also for synthesis in the 

 cytoplasm (Allfrey et al., 1955), a conclusion in accord with classical evidence 

 that the nucleus of Protozoa is indispensable for regeneration (Morgan, 1901; 

 Needham, 1952), but the turnover-rate of thymine (Roll et al., 1950) and of 

 adenine (Hammarsten, 1951), in DNA, is extremely low in the intact liver, by 

 contrast with the rate during regeneration, whereas PNA-turnover is very rapid 

 even in intact liver. 



In addition to earlier examples (Needham, 1952), new instances of the accumu- 

 lation of PNA during the early P-phase of regeneration include those of Aquila 

 (1952) for healing bone, of Barakina (1951) for the limbs of anuran tadpoles, and 

 of Takata (1952) for the lens of the eye of Tritunis. Barakina confirmed earlier 

 observations that the maximal concentration in the epidermis is earlier than that 

 in the deeper tissues, in accord with morphogenetic differences (p. 597). Aug- 

 mentation of PNA, in physiological concentration, accelerates regeneration 

 (Brondsted, 1953) but higher concentrations are inhibitory (Fischer, 1946, p. 219; 

 Needham, 1952 p. 35; Thomas et al., 1952). 



The coarse basophilic PNA-granules of mature cells break down into a fine 

 dispersion during the R-phase (Jacovleva, 1945; Opie et al., 1946; Pirozynski and 

 Von Bertalanffy, 1952) and there may be little actual destruction of PNA during 

 that phase (Needham, 1952, p. 33-4), except in necrotic cells (Stowell and Lee, 

 1950; Pirozynski and Von Bertalanffy, 1952). 



{c) Activities of phosphatases 



The function of acid phosphatase in the R-phase is uncertain, and that of alka- 

 line phosphatase remains even more obscure, probably because in fact it is con- 

 cerned in many processes during regeneration. As a potential enzyme for the 

 transfer of phosphate from organic monophosphates (Danielli, 1951 ; Morton, 1955) 

 it might be active wherever energy is required, at any stage, and available re- 

 cords, collectively, indicate that it is. It is often associated with the nucleic acids, 

 the most important of organic phosphates (Ely and Ross, 1951 ; Rosin, 1952), or 

 with their activity (Brachet and Jeener, 1948) or with that of the chromosomes 

 (Wachstein, 1945), and cell-division may be one of the processes it promotes 

 (Table 9). A large number of workers have found two major peaks in its activity 

 during the course of regeneration (Table 8), and others (Norberg, 1950; Tsuboi 

 et al., 1954) have found more complex fluctuations. This may indicate that it is 

 mainly concerned in the "motor" activities of proteins (Danielli, 1951) and Gould 

 and Gold (1951) concluded that it is not concerned in processes of synthesis. A 

 summary of available records (Table 9) however indicates three main functions 

 (i) in dedifferentiation (2) in cell-division and (3) in differentiation, particularly 

 of collagen. At the molecular level de- and re-differentiation are probably motor 

 processes not very different from muscular and amoeboid movements (Goldacre, 

 1952)5 which again have considerable resemblances (Brachet, 1950, p. 184) to 

 the mechanical processes of mitosis. 



