CONFORMITY WITH PLAN 355 



another, but at the same time unite into one splendid 

 framework. 



The direct influence of the impulses on the protoplasm 

 is specifically different from the reciprocal influence that 

 other natural forces exert on one another ; for the impulses, 

 which do nothing but organise, act on physical and chemical 

 factors already present in the protoplasm. 



Protoplasm is almost unlimited in its formative possi- 

 bilities, and so is almost ideal as a plastic medium. 



But at the present day we do not know why the impulses 

 affect the protoplasm only, nor how they do it. They connect 

 themselves with substances that release processes, and they 

 activate these substances. That is all we can say about it. 



And so the impulses differ from other natural factors 

 in two respects — ^by the way in which they affect the proto- 

 plasm, and by their association into systems. 



The great question of the future will be whether it is 

 possible to isolate the impulses, and force them to influence 

 substances other than protoplasm. Already there are indica- 

 tions that an isolation of the impulses may be effected. Many 

 instances of gall-formation point this way, seeming to suggest 

 the transference of a form-giving impulse from the insect to 

 the plant. The discovery made in Spemann's laboratory by 

 Wachs when working on Amphibia has a like significance : 

 he found that the cells of the upper iris, which do not 

 themselves possess the power to make lens fibres, can be 

 endowed with that power by a secretion coming from the 

 retina. 



I am convinced that cases of this kind, accessible to 

 analysis, will become more numerous as soon as attention 

 is more generally directed to them. 



It is impossible to say whether we shall attain to the ideal 

 I have before me, of inducing form-making to take place 

 within a test-tube. But at any rate we can get much closer 



