2o6 BIOLOGICAL LECTURES. 



intelligent, than to physical and chemical processes as known 

 in the physical sciences. The action seems, however, to be 

 intelligent only so far as concerns the internal relations of the 

 part, i.e., it acts rather as a "perfecting principle" than as a 

 process of adaptation to external needs (adaptation). 



IX. 



Finally, I wish to touch briefly on a few points that seem to 

 me to bring us nearer to the heart of the problem. In much of 

 our biological work we have been guided by methods derived 

 from the physical sciences, and most fortunately so, for per- 

 haps only in this way can we hope to reduce living phenomena 

 to simpler terms. But sooner or later we meet with a factor 

 that defies further physical analysis, and this factor seems to 

 be present in all biological phenomena. We gain nothing by 

 calling it a vital force, unless we can define what we mean by 

 vitality. Whether or not this factor ^ is only a complex of 

 physical forces that we cannot unravel, or whether there exists 

 something that cannot be expressed in terms of physics and 

 chemistry — that is the question! 



We err, I think, in going at present to either extreme, i.e., 

 either in ignoring this something that has been called a vital 

 force and pretending that physics and chemistry will soon 

 make everything clear, or, on the other hand, in calling the 

 unknown a vital force and pretending to explain results as the 

 outcome of its action. 



In our studies of the development of form we meet most often 

 with this factor. Are we at bottom trying to give a causal 

 explanation of form itself, and, if so, is not our problem insol- 

 uble } Can we hope to do more than determine under what 

 internal and external conditions a given form appears .'* If we 

 limit our researches to this problem we can hope to succeed. 

 But can we go back of this and explain the reaction itself 1 At 

 present we have not succeeded in doing so, any more than has 

 the mineralogist explained the form of a crystal. It may be 



1 It is simpler to speak of it as one factor, but it may equally well be true that 

 there are many factors. 



