INTEGRATIVE ACTION OF THE CEREBRUM 955 



The methods employed for the study of these higher integrations of 

 the central nervous system all depend on the reactions of the animal 

 that are associated with the taking of food. When the food is actu- 

 ally placed in the mouth, it excites a secretion of saliva, whatever the 

 circumstances may be. This is an unconditioned reflex. Suppose, how- 

 ever, that every time food is given a particular sound is made; after 

 some time it will be found that the occurrence of the sound alone is 

 sufficient to cause a secretion of saliva. In other words, a conditioned 

 reflex has been formed. Similarly, sight or smell or any other type of 

 sensation may be made the excitant for the conditioned reflex. The 

 secretion now becomes psychic instead of merely physiological. To quote 

 Bayliss: "Any phenomenon of the outer world for which the animal in 

 question possesses appropriate receptors can be drawn into temporary 

 association with salivary secretion, so that it becomes an exciter of se- 

 cretion if only it has been frequently presented at the same time with 

 the unconditioned reflex stimulus, food in the mouth." 



Work along lines similar to that devised by Pavlov has more recently 

 been undertaken by students of animal behavior, who have utilized the 

 acquired habits of an animal in searching for its food in order to study the 

 influence of conditioning circumstances on its procedure. The advantage 

 of this method depends mainly on the fact that it can be applied to all 

 groups of animals. In carrying out such an observation, the animal is 

 placed in one compartment of a cage, from which it is then released to 

 a second compartment, the end of which is divided into two passage- 

 ways, one leading to food, the other leading to some compartment in 

 which the animal is punished for its mistake as by receiving an electric 

 shock. Objects such as colored lights are placed in the different pas- 

 sageways, and the animal by repeated trial comes ultimately to learn 

 which particular colored light signifies the passage along which he 

 will receive food. A reflex has therefore become established conditioned 

 on the particular colored light. 



On account of the unavailability of his publications, it is impossible 

 at present to give any complete account of Pavlov's discoveries. A few 

 facts, however, are of such importance that it is necessary for us to 

 state them here as far as we know them. (See Bayliss, Physiology.) Two 

 mechanisms seem to be concerned in the conditioned reflexes: (1) that 

 of temporary association, and (2) that of analysis. Temporary associa- 

 tion is well illustrated in the above experiment in which the secretion of 

 saliva is induced by a sound. Temporary association of the sound with 

 the secretion of the saliva may readily be inhibited by all kinds of ex- 

 ternal phenomena; thus, if the dog's attention becomes diverted while 

 the conditioned reflex is being stimulated, the response does not occur. 



