SECT. 3] 



AND ORGANISATION 



585 



Absorption 



that the amount of solid absorbed by the embryo during that period 

 was equal to the difference between the size at x and the size atj 

 would be to assume that the efficiency of the embryo was 100 per 

 cent., which is certainly not the case. As the diagram shows, what 

 has actually happened could 

 be represented in abstract form 

 by a peaked curve super- 

 imposed on the growth-curve 

 representing by its upward 

 sweep the total quantity of 

 soHd absorbed during the 

 period in question and by 

 its downward fall the total 

 quantity of solid cataboHsed, 

 or "oxidised", and excreted 

 as carbon dioxide, uric acid, 

 etc. The fact that the down- 

 ward slope does not go down 

 as far as the upward slope has 

 come up is what makes growth 

 possible. The process of growth, then, might be related to that of 

 cataboHsm as rival, not as offspring, and instead of resulting from it 

 might compete with it for the available solid substance. Or, on the 

 other hand, the steeper the curve the higher the peaks might be above 

 it, in which case metaboHc rate would be highest when growth-rate 

 is highest. Everything depends on the relative magnitudes. The 

 experimental fact that the metaboHc rate of the whole embryo is 

 highest when the growth-rate is also highest reveals no simple causal 

 nexus between them, and it is not theoretically correct to assume 

 such a relation. 



Child has used various methods to ascertain the existence and 

 distribution of his gradients: 



Fig. 95- 



(I 



(2 



(3 

 (4 



(5 

 (6 

 (7 



Direct susceptibility. 



Indirect susceptibiUty. 



Reduction of potassium permanganate. 



Formation of indophenols. 



Observation of electrical potential. 



Estimation of carbon dioxide produced. 



Estimation of oxygen taken in. 



