VII INTERNAL FACTORS 635 



(Goldner, 1925) and fat-soluble extracts of the "gland" accelerate the healing of 

 bones in the rat (Eskelund and Plum, 1953). Extracts of other lymphatic tissues, 

 of spleen and of adrenals are inactive so that the effect is not simply that of a 

 lymphoid tissue, stimulated in the normal way by the S-corticoids (p. 631), during 

 the G.A.S. (Selye, 1948). 



(v) Parathyroid. Because of its connexions with calcium metabolism, parathyroid 

 activity naturally is essential for bone-healing (Greep, 1949) and possibly more 

 generally (Arey, 1936), but there is little detailed knowledge of its action specifi- 

 cally during regeneration. 



(vi) Insulin. Like APGH, insulin improves nitrogen-retention and normal 

 growth (Fischer, 1946; Sevag et al., 1950; Gaunt, 1954) but again a positive action 

 on regeneration is not universally admitted (Arey, 1936), though healing is 

 generally fovmd to be slow in diabetics (Marshall, 1952). During the early stages of 

 post-traumatic stress there are symptoms of diabetes (Green and Stonor, 1954), 

 associated with adrenal steroid-activity, and insulin in fact reduces that increase 

 in amino acid-content of the blood following hepatectomy (Flock et al., 1953). Like 

 APGH it is probably normally most active during the P-phase. 



{vii) Hormones in invertebrates. The corpus allatum (Wigglesworth, 1954) is neces- 

 sary for normal regeneration in larval insects; extirpation of the gland results in 

 inhibition (Bodenstein, 1953a) or in abnormal proliferations (Pflugfelder, 1939). 

 This might have been expected (p. 596) of the "juvenile" hormone. The corpus 

 allatum seems to change its general action when the insect undergoes metamor- 

 phosis (Wigglesworth, 1954; Bodenstein, 1953b) and this applies also to its action 

 on regeneration (Bodenstein, 1955): extirpation of the gland in the imaginal 

 cockroach now permits regeneration of amputated limbs. Regeneration occurs 

 even in limbs amputated some time before allatectomy (Bodenstein, 1955), — a 

 very elegant demonstration that a wound-factor is irrelevant to regeneration in 

 Arthropoda (p. 626). 



The prothoracic, "growth and differentiation", hormone of insects is believed 

 to promote regenerative growth also (O'Farrell and Stock, 1954). In the cockroach, 

 Blatella germanica, the prothoracic gland shows a sharp burst of mitoses in the 

 middle of the stadium (p. 599) which is 5-6 days long. A burst of mitoses follows 

 in the tissues of the body, the epidermis in particular, and the onset of ecdysis is 

 then irreversibly determined. However if limbs are amputated before this critical 

 period the next ecdysis is delayed by a period equal to that which has already 

 elapsed between the previous moult and amputation, so that a fully differentiated, 

 and almost full-grown, regenerate is eclosed at the next moult. If amputation 

 occurs after the critical period, then moulting is not retarded, and the regenerate 

 appears only as a small blastema. Before the irreversible stage, therefore, ampu- 

 tation, or its consequences, is able to "put back the clock", — perhaps to delay ac- 

 tivity in the prothoracic gland, — and so to cover the earlier R-phase of regenera- 

 tion in time to benefit from this growth-promoting activity. 



It might seem to follow from the precise amount of the delay induced that the 

 normal arthropod growth-cycle in each stadium resembles the regeneration cycle, 

 and it is perhaps significant that there is a period of nitrogen-flow after moulting 

 and one of low N-output before moulting (Needham, 1957 and subsequent work). 



Lileraiure p. 64IJ 



