E. A. ASRATYAN 



103 



nervous structures corresponding to (P) (i.e. the alimentary stimulus). 

 This is clear from the fact that passive lifting of the leg or local cooling 

 of the skin also acquire a signalling significance (i.e. the faculty of evoking 

 an alimentary reaction in a conditioned reflex way when repeatedly 

 combined with food, according to the method of 'covering' applied in 



^ -nrr 



l u iiiiiiiii in i um i ini i mm i nm i nii i u i mi iiiii m i 



197(20) 



nj\JiJi_AJi_n_n_n-JuriJv-n_n_a_rLJLruvn_n_n_n_rij^^ 



a 



6 



Fig. 5 



{a) A motor conditioned reflex evoked in the dog by the act of eating (direct connection); 

 (/)) an ahmentary reflex evoked by the passive lifting of the leg (reverse connection). 



I. — Mark of masticating movements; 2. — mark of placing the leg on a bench; 3. — mark 

 of movements of the same leg; 4. — mark of salivation ; 5. — mark of passive movement of the 

 leg ; 6. — mark of presentation of food (figure indicates the number of combinations) ; 

 7. — mark of time — in seconds. 



the experiments discussed above. This is demonstrated in Fig. 6. The 

 data obtained from these experiments show that here too there is a 

 considerable difference between the specific features of direct and reverse 

 conditioned connections, and that, furthermore, it is the same kind of 

 difference as is observed when two 'indifferent' or two unconditioned- 

 reflexes are combined. Thus, in a given case the direct conditioned reflex 

 connection is formed more rapidly than the reverse conditioned reflex 

 connection and is much more powerful, stable and effective. 



The fact demonstrated by Struchkov that only weak and unstable 

 conditioned reflexes become indifferent stimuli when 'covered' by un- 

 conditioned reflexes, has been known since the work of Pimenov (1908), 

 Krepa (1933), Pavlova (1933), Vinogradov (1933), Petrova (1933) and 

 others; but these authors regarded it as an indication of the elaboration of 

 an ordinary one-way conditioned reflex connection possessing certain 

 specific features. In Struchkov's experiments this fact appears in quite a 



