VI 



GROWTH OF MAMMALS 



223 



protein loss, transition from metabolically active mass to metabolically inactive 

 differentiations has to be taken into account (Bertalanffy, ig5ia; cf. p. 208). 



{c) Embryonic growth 



For the reasons discussed previously (p. 140), growth as quantitative increase 

 of the organism and its organs is a rather superficial aspect of embryonic develop- 

 ment which proceeds with determination and segregation of embryonic areas, 



other tissues 

 Blood 



Skin and wool 



Brain 

 Kidney 

 Heart 

 Lung 

 In test. 

 Liver 

 Musculature 



Skeleton 



72 78 80 



97 100 104 no 112 

 Fetal age 



130 135 140 

 days 



Fig. 28. Growth of organs in the sheep embryo. Weight of subsequent organ was added to 

 the prior one; highest hne represents total weight. After Barcroft from Bertalanffy, 1957. 



formative movements, elaboration of organs and histological differentiations, etc. 

 Thus it is easy mathematically to fit embryonic growth by suitable formulas, but 

 these hardly have much physiological significance. 



Frequently embryonic growth curves can be approximated by simple exponen- 

 tial curves (Brody, 1945). If plotted semilogarithmically, breaks in the straight 

 lines representing exponential growth appear simultaneously in the various organs 

 (Fig. 28), so showing that physiological changes take place in these periods. 



According to Hugget and Widdas (1951) embryonic growth frequently can be 

 fitted by the empirical equation: 



w^'^ = ct (6.1) 



Literature p. 253 



