2l8 



GROWTH 



PRINCIPLES AND THEORY 



Laboratory experiments show the same dependence of body size on temperature 

 (Table 13). No experimental postembryonic growth curves in dependence of temperature 

 have been found in the literature, including the extensive monograph by Precht, Christo- 

 phersen and Henzel (1955). The only available data apparently are those of Gibson and 

 Hirst (1955) on the Guppy {Lebistes reticulatus) which are incomplete because they only 

 reach to the time of sexual differentiation, and growth of males and females (strikingly 

 different in the Guppy, cf. p. igSf.) was not further followed. However, the description given 

 reveals the characteristics mentioned: while a water temperature of SS'^C is noxious 

 (all fish develop crooked spines) and one of 25°C is optimal, /. growth rate at 30°C is 

 faster than at 20°C; and 2. females developing at 30°C are much smaller than those 

 at 20°C. 



VI. GROWTH OF MAMMALS 



[a) Postembryonic growth 



Growth in mammals shows a number of complications, both with respect to 

 metabolic and growth rates. 



Rubner's surface rule of metabolism was first stated for mammals. However, more recent 

 investigation has shown that the relation between body size and metabolic rate is more 

 complex. In intraspecific comparison of the best-investigated laboratory animal, the rat, a 

 crude overall relation of respiration to the 2/3 power of weight can be found. Detailed 

 study, however, shows a break in the allometric regression line so that up to approximately 

 100 g body weight metabolic rate increases more, and afterward less than would correspond 

 to the surface rule (Fig. 23) (Racine, 1953). The break corresponds to the onset of sexvial 

 maturation. In interspecific comparison of mammals of different species, metabolic rate varies 

 with the 3/4 power of body weight, rather than with the 2/3 power as would correspond 

 to the surface rule (Brody, 1945; Kleiber, 1947). 



10 15 20 



30 40 5060 100 200 



Body weight in g 



400 



Fig. 23. Discontinuities in the allometric curve. The figure shows some phenomena of 

 relative growth in the albino rat. All discontinuities occur at a body weight of approx. 

 100 g, i.e. before puberty. A corresponding discontinuity is found in the growth of the 

 entire animal (Fig. 26). The figure only gives regression lines; complete data and statistical 

 analysis in: Bertalanffy and Pirozynski, 1952, (relative growth of liver and thymus); 

 Racine, 1953 (basal metabolic rate for males); Bertalanffy and Pirozynski, 1953 (Qoj)- 



