EVOLUTION 185 



to produce results, there is still lurking an element of 

 chance, which simply means an unknown and hence 

 uncontrolled factor. Even when the factors are well in 

 hand and we can combine them with reasonable cer- 

 tainty that the result will appear, we may be entirely 

 wrong in our conclusion as to what in the combination 

 has produced the result. 



For example, we have been changing the forms of 

 certain plants at will by supplying in their nutrition 

 varying combinations of certain substances. By manip- 

 ulating the proportions of these substances we pro- 

 duce the expected result. It was perhaps natural to 

 conclude that the chemical nature of these particular 

 substances produce the result, and our prescription was 

 narrowed down to certain substances. Now, however, 

 it is discovered that the results are not due to the chemi- 

 cal nature of these substances, but to a particular physi- 

 cal condition which is developed by their combination, 

 a condition which may be developed by the combination 

 of other substances as well; so that our prescription is 

 much enlarged. In this operation we are thus freed 

 from slavery to particular substances, and must look 

 only to the development of a particular physical con- 

 dition. 



It seems to me that there is a broad application 

 here. In education, we are in danger of slavery to 

 subjects. Having observed that certain ones may be 

 used to produce certain results, we prescribe them as 

 essential to the process, without taking into account 

 the possibility that other subjects may produce similar 

 results. 



