230 



GROWTH 



PRINCIPLES AND THEORY 



finds at least a partial, physiological confirmation and explanation in the principle 

 of allometry. 



There is a competition of organs for material as expressed in equation (7.5) 

 which also indicates that the "struggle of the parts" (Roux) can be represented by 

 a simple mathematical law. Thus the principle of allometry gives a physiological 

 and quantitative basis to the morphological principle of the "balance of organs". 



30 40 50 60 80 100 150 200 300 400 

 Body weight in g 



Fig. 32. Relative growth (postnatal) of some organs of the albino rat. The figure shows 

 only the regression lines; observed values and statistical analysis see original. After Berta- 



lanffy and Pirozynski, 1952. 



(c) Physiological competition 



The competition for material, which is also important, in evolutionary changes, 

 as compensation of organs (p. 246f.), can be interpreted biochemically to a 

 certain extent. One critical factor determining mitotic rate is supply of energy in 

 the form of glucose. Tissues apparently are competing for the available glucose 

 supply, especially under conditions of carbohydrate deficiency (Bullough, 1952). 

 Such competition exists between adjacent as well as distant tissues. An example 

 of the first is that a wave of hair growth induces inhibition of the mitotic activity 

 in the epidermis, particularly involution of warts; similarly, activity of the 

 mammary glands during the lactation period induces a reduction of mitotic 

 activity in hair formation. The second is exemplified by embryos and tumors 

 which have the highest priority in the competition for nutritive material and 

 continue to grow even when the rest of the body is almost reduced to a skeleton. 

 According to Bullough the greatest competition to mitotic activity is probably 



