Explanatory Notes 117 



molecular collision, seems to be clear; but the cause of it 

 may be put differently by different people. (See pages 37 

 and 38.) 



Pages 29 and 30 



The reference here is to the extreme doctrine of Professor 

 Weismann, at one time urged upon us, that no character- 

 istic acquired during the life of an individual or series of 

 individuals could be transmitted by inheritance. The 

 truth underlying this doctrine is that unless the sperm or 

 germ cells are affected, mere alteration of body tissue is 

 ineffective for anything beyond the individual. That is 

 manifest. The cells which transmit vitality to the off- 

 spring must naturally be modified if modifications are to be 

 conveyed by them. But it is unreasonable to suppose that 

 deep-seated changes in somatic or bodily structure can be 

 caused without at least running the risk of affecting the 

 more permanent transmission cells also to some extent. 

 Mere defective or injudicious nourishment may have its 

 due influence in this direction. A microscope may not 

 show any difference, some other test must be applied ; and 

 by far the most sensitive test for the actual occurrence of 

 such alteration consists in observing whether inheritance is 

 really affected or not. On that question specific experi- 

 ments are desirable and ought to be made. If surround- 

 ings have no effect on the race, except a survival effect, 

 if the individual can acquire nothing which is transmissible, 

 it will be very extraordinary; but the test can only be 

 made by direct experiment and observation. Hence we 

 are thrown back on actual experience in every instance, 

 and we cannot generalise and say that no sort of character 

 acquired by the individual can be handed down to his or 

 her descendants. What I suggest in the text is that the 

 discontinuity between reproductive and bodily cells is not 

 likely to be as complete as that. 



