158 EVOLUTION AND GENETICS 



The latest experiments (which are not yet fin- 

 ished) show that the conditional reflexes, i.e., the 

 highest nervous activity, are inherited. At present 

 some experiments on white mice have been com- 

 pleted. Conditional reflexes to electric bells are 

 formed, so that the animals are trained to run to 

 their feeding place on the ringing of the bell. The 

 following results have been obtained : 



The first generation of white mice required three 

 hundred lessons. Three hundred times was it neces- 

 sary to combine the feeding of the mice with the 

 ringing of the bell in order to accustom them to run 

 to the feeding j^lace on hearing the bell ring. The 

 second generation required, for the same result, only 

 one hundred lessons. Tlie third generation learned 

 to do it after thirty lessons. The fourth generation 

 required only ten lessons. The last generation which 

 I saw before leaving Petrograd learned the lesson 

 after five repetitions. The sixth generation will be 

 tested after my return. I think it very probable that 

 after some time a new generation of mice will run 

 to the feeding place on hearing the bell with no 

 previous lesson. 



Until we have a full account of Pawlow's meth- 

 ods it msLj be safer to wait before interpreting his 

 results ; but this is by no means a new topic, for al- 

 ready the effects of training and its possible inherit- 

 ance had been examined bv three American investi- 

 gators who used the most approved methods that 

 experience has taught are essential in obtaining data 



