368 SERGIUS MORGULIS 



physiological activity as, for instance, the activity of the salivary 

 gland. This association is brought about by repeatedly combining 

 that factor with the physiological stimulus of the gland (food, 

 acid) . When after a time such a connection is formed the particu- 

 lar factor which previously had no relation to the salivary gland 

 now affects it as a stimulus. It is very significant that at the 

 moment when this connection first becomes established any 

 stimulus from the same receptive surface acts as a conditioned 

 stimulus of the gland. But as the particular stimulus — smell, 

 sound, light, etc. — is repeatedly applied simultaneously with or 

 in a definite time relation to the feeding, the response of the animal 

 becomes more and more specialized. We distinguish, thus, two 

 phases in the formation of the conditioned reflexes which are so 

 constant as to justify their formulation as two definite laws. 

 The first is the law of radiation of nervous processes in the brain. 

 This may be pictured to one's self so that every stimulus upon 

 reaching a definite sensory cell in the cortex of the hemispheres 

 diffuses over the entire centre. The law of radiation may be 

 demonstrated by an old physiological experiment. If a definite 

 region of the cortex is stimulated a short time, a certain set of 

 muscles is thrown into contraction. If, however, the stimulation 

 cont'nues, it diffuses, radiates over a larger area and at last over 

 the entire cellular mechanism of the cortex, whereby many other 

 groups of muscles become gradually involved in the reaction. 

 The stronger the irritation of any particular point of the cortex 

 the wider it diffuses and the more it subordinates to its influence 

 other less irritated elements. It is interesting to note that in the 

 very extensive experiments on conditioned reflexes it has been dis- 

 covered that if the desired stimulus is applied about ten seconds 

 before feeding and is continued during the feeding the reflex 

 will be formed after a few trials. If, on the contrary, the dog 

 is first fed, then, ten seconds later, the stimulus is applied as 

 usual, the desired conditioned reflex cannot be established, no 

 matter how often and persistently this combination is tried. 



Parallel to radiation an opposite phenomenon invariably 

 occurs, and this is expressed in the second law of the concentra- 

 tion of nervous processes. In this way, by continued repetition, 

 the diffused auditory reflex becomes so differentiated and concen- 

 trated that the stimulation of 1,012 vibrations may be received 



