Considerations on the Problem of Learning 145 



that reactions to disagreeable stimuli should be- 

 come reduced the more often they occur. If a re- 

 ceptor is connected with neurones A, B, C, and D 

 involved in a reflex response to a stimulus that pro- 

 duces disagreeable effects and an avoiding reaction, 

 then as the neurones are, ex hypothesi, injuriously 

 affected, the intimacy of their synapses would be 

 weakened and the course of the impulse through the 

 system more or less blocked. The disagreeable ef- 

 fects and the vigor of the avoiding response would 

 therefore tend to wear away after successive repeti- 

 tions. In general it cannot be said, I think, that 

 this occurs. Castor oil ought, after being taken a 

 few times, to become much less unpleasant, but I 

 very much doubt if this is a common experience. 

 People suffer pain from a particular region for 

 years with little or no diminution of intensity, and 

 there are some things which up to a certain point 

 may become more disagreeable, instead of less so, 

 the more often they are experienced. Sometimes, it 

 is true, things which are at first disagreeable come 

 to be tolerated in time with little discomfort, but 

 this is probably because the incoming stimuli be- 

 come connected with other neurones than the ones 

 which gave the original motor expression. In other 

 cases it may be due to quite different organic ad- 

 justments. It is doubtful if where the unpleasant 

 stimuli continue to be responded to through the 

 same channels, there is in general a weakening of 

 the response or mitigation of its disagreeable qual- 



