LIFE; BODY AND MIND 211 



made themselves at home in human habitations, 

 like the chimney swallows; yet chimneys are a 

 recent invention. You must all have noticed that 

 in the early days of automobiles, when they were 

 but few and traveled at low speeds, there was 

 relatively far more destruction of hens and 

 other domestic animals by automobiles than 

 occurs now. These cases may perhaps be ex- 

 plained, however, by some sort of mutual in- 

 struction. 



Yet the number of such observations, al- 

 though no single one would be worthy of much 

 notice, has led a number of investigators in 

 recent years to plan definite experiments to test 

 the transmission of newly acquired mental 

 habits. Pavloif made a preliminary statement 

 some years ago regarding some experiments of 

 great interest, in which successive generations 

 of mice, each subjected to the same training 

 process, showed a remarkable increase in the 

 rate of learning in the later generations. But 

 he does not say how he excluded the possibility 

 that the animals were being educated by one 

 another. Experiments of this sort, which have 

 in view the overthrow of so firmly established 

 a dogma as the non-transmission of acquired 

 characteristics, must be impeccable. Many years 



