232 



GROWTH 



PRINCIPLES AND THEORY 



tively insufficient, regenerates are not harmonically reduced in size; rather toes of approxi- 

 mately normal size but reduced number develop. This is the case in treatment with 

 colchicine which, as a mitotic poison, causes reduction of the regenerative blastema. Toes 

 gradually disappear following an order of priority in the way that the toes formed latest in 

 normal development are reduced most because building materials are already appropriated 

 by those parts which have developed first. This experimental reduction in the number of 

 toes can be compared with phenomena of rudimentation of toes in evolution (Bretscher, 

 1947, 1949; Tschumi, 1953, 1954). 



{d) Biocheinical applications 



The principle of allometry further applies to changes in the chemical composition 

 of the animal body during development. If, for example, ash content is plotted 

 against dry weight, the slope of the allometric line (constant a) is the same in 

 animals as different as the chick, selachians and cephalopods (Fig. 34). Similar 

 relations are foimd in other groups of organic compounds. The species compared 



1000 



■b 10 — 



Scyllium canicula' 

 • Torpedo ocellata 

 « Torpedo marmointa 

 oMustelus vulgaris 



'■ 100 

 mg dry weight (rat) 



10 y^ ^10 100 



mg dry weight (cephalopod and insect) 



Fig. 34. Chemical allometry: Changes in ash content in various animal classes. After 



J. Needham, 1934. 



are different with respect to morphological form, absolute size, nutritional factors 

 and time required for the changes in composition, 'The fact that the law governing 

 such changes and expressed by the allometry constant is the same under so 

 diverse conditions indicates a "chemical groundplan" (J, Needham, 1934) of the 

 organism transcending taxonomic borders. The chemical constituents of the 

 organism appear to tend toward a state of equilibrium or rather steady state which 

 is based on the nature of the "living mass" and hence independent of taxonomic 

 position and differences. 



[e] Physiological applications 



All physiological phenomena hitherto investigated follow the allometric relation 

 in their dependence on body size (Adolph, 1949). That is, plotting metabohc 

 rate, respiratory or pulse frequency (Fig, 35), excretion, enzyme content, or any 

 other physiological magnitude against body size, an allometric line is obtained, 

 which either covers the total range or, if breaks occur, these are related to 



