CONDITIONED AND UNCONDITIONED REFLEXES 859 



during this interval of inhibition some other sensory stimulus is applied, 

 it will be likely to cut short the inhibition; in other words, it produces 

 an inhibition of inhibition, so that the secretion of saliva occurs. 



Another most curious combination of conditioned stimuli is illustrated 

 in the following experiment. Suppose, for example, that a given light 

 and sound are each separately made a stimulus for a conditioned reflex, 

 but that when they occur together there is no reflex. Suppose now that 

 while one of these active stimuli is being presented, the other stimulus 

 is also presented; the result will be that the secretion produced by the 

 one stimulus will stop. Evidently, although each is in itself a stimulus, 

 acting together they cause inhibition. 



By studying the conditioned reflexes after a certain part of the cere- 

 bral cortex has been removed, it has been found that the power of estab- 

 lishing certain kinds of conditioned reflexes becomes abolished, while 

 that for others is retained. 



