E. A. ASRATYAN 99 



classical unconditioned stimuli of moderate intensity, namely, presentation 

 of food and electrical stimulation of the leg. She established the possibility 

 of elaborating a stable double (or two-way) conditioned connection be- 

 tween cerebral nervous structures corresponding to these two stimuli. It 

 should be noted that under standard experimental conditions (strictly 

 alternating sequence of combination of stimuh, relative equality of their 

 intensity, observance of the routine conditions of maintenance of the 

 experimental animal, etc.) these conditioned connections are practically 

 equivalent as regards sign, strength, stability and so on. 



On the contrary, in the experiments of Lyan-Chi-an, two unconditioned 

 stimuli were combined in a stereotyped sequence. In other words, he 

 combined in a stereotyped sequence a defensive motor reflex of a fore-leg, 

 evoked by applying an electric shock of moderate intensity, with an 

 alimentary reflex to the presentation of a moderate portion of powdered 

 meat and bread. In certain series of experiments, performed on one group 

 of dogs, application of the electric shock preceded presentation of food, 

 while in other series, performed on another group, presentation of food 

 preceded application of the electric shock. Both series of experiments 

 yielded essentially similar results which agree in some respects with the 

 data of Varga and of Pressman and Varga, but differ in some essential 

 points. In the experiments of Lyan-Chi-an, double (or two-way) con- 

 ditioned reflex connections between the brain points of the combined 

 unconditioned stimuli were also formed. This is shown in Figs. 3 and 4. 

 However, here also, as in the similar Varga and Pressman experiments, 

 direct and reverse conditioned comiections between these points were far 

 from being equivalent. In comparison with Varga and Pressman's 

 experiments those of Lyan-Chi-an showed a considerably more pro- 

 nounced difference in the rate of elaboration of conditioned connections 

 leading from the preceding (P) to the subsequent (S) stimulus, than from 

 (S) to (P). In both scries of Lyan-Chi-an's experiments, the direct condi- 

 tioned reflex connection between the combined unconditioned stimuli is 

 formed sHghtly more rapidly than the reverse conditioned reflex connec- 

 tion. This connection is also of much greater strength and stability and is 

 characterized by a considerably greater regularity than the reverse connec- 

 tion. In contradistinction to a direct connection between two indifferent, 

 i.e. physiologically weak stimuli, a direct connection between two un- 

 conditioned, i.e. physiologically strong stimuli, forms easily, consolidates 

 increasingly from day to day and persists if the conditions which have 

 given rise to it are maintained; namely, when these stimuli are combined 

 in the given sequence. 



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