VII 



INTERNAL FACTORS 645 



More than one factor may be involved in vascular controls. The hypertrophy of 

 a kidney after unilateral nephrectomy is slower and more prolonged than the 

 rise in blood-urea (Warburton, 1955). This might be a simple inertia-phenomenon, 

 but a kidney which atrophies because its ureter is ligatured, remains functional 

 if, in addition, the partner-kidney is removed (Hinman and Butler, 1923). In a 

 closely similar manner a lobe of the liver will atrophy if its portal blood-supply 

 is ligatured, but not if the bile-outflow from the rest of the liver is obstructed 

 (Rous and Larimore, 1920). Compensatory hypertrophy of liver and kidney also 

 depends on the amount of dietary protein in need of deamination (Rous and Lari- 

 more, 1920). 



Most of the numerous systemic changes of the GAS depend on vascular control and 

 many other examples, more peculiar to regeneration, have been cited in this chapter : for 

 instance an increase in plasma-phosphatase during liver-regeneration (Taleisnik, 1954), 

 a mobilisation of depot-fat (Yarbro and Anderson, 1954), and the transport of sulphydryl 

 compounds from the liver to regenerating skin (Schacter et al., 1952; Beck and Linken- 

 heimer, 1952; Williamson and Fromm, 1955). Peptidase activity is increased in the blood 

 leaving an injured region (Selye, 1948). Similarly neoplasms induce an increase in ca- 

 thepsin activity throughout the body (Maver et al. 1948). It is noteworthy, however, that 

 methionine and cystine from the liver go only to regenerating skin and not to normal skin 

 or to other organs (Williamson and Fromm, 1955). This unilateral type of vascular effect 

 may prove to be more common. Hormones are well known to affect particular "target" 

 organs (Gaunt, 1954). 



(/) Diffusing factors 



In such avascular Metazoa as the Platyhelminths this type of factor is to be 

 expected (Lender, 1952 ; Brondsted, 1955) but even in vascularised animals diflfus- 

 ing factors seem common. Calcium for bone healing is mobilised mainly locally 

 and in declining amount with distance from that point. Dedifferentiation, more 

 generally, follows the same pattern (Thornton, 1954) though it may "skip" 

 resistant regions such as the head of a bone. There is a mutual stimulation of 

 regeneration between hind-limb and tail-blastemata of Urodeles provided they are 

 grafted within a critical distance of each other (Blacher et al., 1 933) ; mechanical ob- 

 stacles, as well as mere distance, reduce the effect. The interaction between regen- 

 erating arthropod-limbs similarly decreases with distance. Neoplasms inhibit 

 regenerates in proportion to their nearness (Zdriukovskaja, 1942) and so do 

 gonads, in Hydra (Goetsch, 1929). Abeloos (1953) was unable to detect either 

 nervous or vascular control of the phenomenon of reversal of operculum-types in 

 Hydriodes, and Ludwig and Ludwig (1954) concluded that diffusing factors were 

 involved. 



Diffusion seems not only the primitive mode of coordination, but also the most 

 efficient method of controlling the pattern of differentiation and differential 

 growth, throughout the regenerate and the neighbouring stump-tissues. In plana- 

 rians morphallactic changes throughout the body may be controlled in this way. 

 The qualitative aspects are not strictly relevant here (p. 595). There is much 

 evidence of interaction between the various local tissue-components, throughout 

 the act of regeneration, and these in general must depend on diffusion-effects. 



It was concluded (Needham, 1952) that the epidermis controls the early stages 



Literalure p. 64^ 



