SECT. 3] 



AND ORGANISATION 



551 



Murray's presentation of the facts does bring an order into a realm 

 where order is much needed. But it is not ahogether easy to see why 

 increase in dry weight should be regarded as "chemical growth", for 

 water is just as much a chemical compound as anything else. Why should 

 the title of chemical compound be restricted to those bodies which 

 do not happen to be liquids at room temperature? And the wetness 



Deyas 



11 13 



Incubation age 



Fig. 94- 



of the embryonic body must also exercise a profound influence on 

 the speed and nature of the chemical reactions going on within it, 

 as is emphasised in the work of Ruzicka and his school. There is 

 therefore some reason for objecting to the term "chemical growth", 

 though the simple fact that rate of increase in dry weight follows an 

 opposite course from rate of increase in wet weight (i.e. "growth") 

 is plainly of importance. There is less reason for objecting to the 

 term "chemical differentiation", for Murray uses it to refer to such 

 entities as percentage of ash and percentage of fat, and shows that, 

 although for by far the greater part of the embryonic period the 



