CONTRIBUTIONS FROM PAWLOW'S LABORATORY 367 



remarkable, because the delicate adjustment of the organism to 

 its environment through its elaborate system of analysers was 

 interrupted at one essential point. The immobility of the dog 

 is apparently of the same origin, as it is believed that the locomo- 

 tor activity, which is a succession of reflexes, begins with the 

 stimulation of the skin of the soles, which in this specimen is 

 incapable of intermediating between the inner and the outer 

 world of the animal. 



The conditioned salivary reflex to auditory stimuli formed 

 before the extirpation of the tactile region in the hemispheres 

 retains its full strength in the operated dog. Furthermore, new 

 conditioned reflexes can be formed after the operation, showing 

 that the function of the central nervous system remains normal 

 wherever the mechanism of stimulation and response is intact; 

 where this mechanism is impaired there is lack of function. To 

 the psychologist this animal with the central part of the tactile 

 analyser missing is a complete enigma. From his angle the 

 animal appears as an irreconcilable contradiction, being abnormal 

 in one environmental relation, and entirely normal in another. 

 But from the objective, analytical point of view, this is very 

 plain, the dog behaving normally where the paths of communi- 

 cation, with the outside world are physiologically uninterrupted. 



The problem of the localization of functions in special centres 

 of the brain suggests itself here. If an animal with some specific 

 brain defect is observed for a long time it is noticed that the defect 

 wears off in time. Complete recovery probably never occurs, 

 but the disturbed equilibrium with the environment is more or 

 less restored. No matter how seriously the brain has been 

 infringed upon, its integral function returns again. This would 

 indicate that the old idea of the large hemispheres as a unit, 

 superseded in 1870 by the theory of localization, is now to be 

 revived. The investigation of conditioned reflexes brought 

 out very clearly the wide range of substitution occurring in the 

 brain after extirpations. There is as yet no information as to 

 the nature of this substitution, but possibly it is to be traced to 

 the same common cause which underlies the generalization of 

 newly developing conditioned reflexes, as will be shown presently. 



We will now examine the various phases in the formation of 

 a conditioned reflex. Any external factor acting upon an ana- 

 lyser may be brought into temporary association with a definite 



