146 INTRODUCTION TO SCIENCE 



(2) It is not a conclusive argument, perhaps, 

 but one of some weight, that if we have not yet 

 succeeded in giving a physico-chemical descrip- 

 tion of a simple vital process, such as the passage 

 of digested food from the alimentary canal into the 

 blood, or the filtering of the blood by the kidney, 

 we need not at present seriously concern ourselves 

 in regard to the possibility of giving a physico- 

 chemical description of growth, cyclical develop- 

 ment, or every-day behaviour. If we think of 

 development for a moment, we cannot but feel 

 that the questions which the facts raise seem 

 very unlikely to receive an answer in terms of 

 mechanism. How are the heritable characters 

 of the race summed up potentially within the 

 minute germ cells? How do they gradually find 

 expression in the individual development, so that 

 ivhat we call differentiation results? What is the 

 nature of the compelling necessity that mints and 

 coins the chick out of a drop of living matter? 

 What is it that regulates the ordered progress 

 which, by intricate and often strangely circuitous 

 paths, leads to the fully-formed organism? It is 

 certainly wonderful the individual unpacking of 

 the racial treasure-box! 



(3) But the most satisfactory reason, perhaps, 

 is the one referred to in the chapter on Scientific 

 Method, that the results of applying physico- 

 chemical analysis to the activities of living crea- 



