CONTRIBUTIONS FROM PAWLOW'S LABORATORY 377 



reactions. For a long time they are received as a single stimulus and only by long 

 continued tests may the differentiation be achieved. This suggests close intimacy 

 of " cold " and " heat " centres in that the component nerve cells are not grouped 

 to form separate centres but are interspersed. This explains the generalized char- 

 acter of heat or cold stimulation. 



Folbort, G. V.— Inhibitory Conditioned Reflexes. 



A conditioned inhibitory reflex has been established in the ordinary way by com- 

 bining repeatedly an inactive stimulus with the natural inhibition of conditioned 

 reflexes. After a while such neutral stimuli become active inhibitory agents. This 

 fact is of much theoretical importance as it shows that a factor acting upon the ner- 

 vous system is stamped by the prevailing process : it becomes a conditioned inhibi- 

 tion, if it happens to coincide with the inhibitory function ; or it becomes a secondary 

 conditioned reflex if it coincides with another phase. Author concludes that the 

 waning of conditioned reflexes is an active process similar to the conditioned inhibi- 

 tory process. 



The indifferent factor, by coinciding with a conditioned reflex which is in a phase 

 of decline owing to intrusive relations, acquires an inhibitory role over all conditioned 

 reflexes. 



Rojanski, N. A.— Materials to the Physiology of Sleep. 



Former investigations of this subject are defective because they deal usually not 

 with normal but induced sleep and sleep-like conditions, and besides do not clearly 

 differentiate the question of the periodicity of sleep or the mechanism of falling 

 asleep and awakening. The author studied last phase of the problem with the aid 

 of method of conditioned reflexes. From the objective point of view, the nature of 

 nervous processes during sleep as they are revealed in the muscular relaxation and 

 reaction to the outside influences must form basis of definition of sleep. As an 

 objective indicator of sleep the relaxation of the eye and neck muscles and the cessa- 

 tion of all conditioned reflexes have been used. The depth of sleep is measured by 

 the degree of muscular relaxation which is determined by an instrument devised by 

 the author. The disappearance of the conditioned reflexes is ascribed to the devel- 

 opment of inhibition. Mechanical interference with bodily movements acts as a 

 hypnotic influence, and it is believed that spontaneous sleep likewise has its origin 

 in the inhibition of movement. Correspondingly stimuli affecting the muscular 

 system are most potent in disturbing sleep. Conditioned muscular reflexes are, 

 therefore, more effective than the conditioned salivary reflex. Stimuli originating 

 in the urinary bladder or in the thick intestine, both of which are associated with the 

 motor system, are very effective agents in disturbing sleep. The principal source 

 of inhibition is in the motor analyser and spreads secondarily by radiation to other 

 parts of the central nervous system. 



The question of the periodicity of sleep must still remain open. It probably 

 depends upon some unknown organic function which periodically favors the radia- 

 tion of inhibition. 



Unconditioned reflexes during sleep increase in strength at first, then diminish 

 below the normal level to increase again just before awaking. Conditioned 

 reflexes wane very rapidly at the beginning of sleep and gradually increase about the 

 time of waking. The physiological source of sleep is the inhibiting developing 

 within the motor analyser. Spontaneous sleep occurs when such an internal in- 

 hibitory process is favored by mechanical resistance to motor impulses. The environ- 

 ment, in that event, acts as a sum of brakes. By removing parts of that environment 

 it is possible to offset partially this inhibitory influence. 



Active animals employed for the conditioned reflex studies were strapped to the 

 stand so that they could not move a limb. The primary object was thus achieved, 

 the animal having become absolutely quiet, but it is useless for the experiment as 

 it soon falls asleep in this environment. The environment becomes a conditioned 

 inhibition. Every time the dog is placed in the stand and strapped the established 

 conditioned reflexes fail to appear. The effect of the environmental gradient is 

 clearly shown by the following experiment. 



