THE HISTORICAL DEVELOPMENT OF NEUROPHYSIOLOGY 



53 



FIG. 39. Ivan Michailovich Sechenov and his diagram illustrating reflex arcs in the spinal cord 

 and brain of the frog, a-b-c-d represents a spinal refle.x arc with sensory (a-A), central (b-c) and 

 motor ((■-(/) components. The reflex arc of the brain consists of the sensory nerve (O), the central 

 component (.V-f) and the motor efferent (<:-(/). P is the region in the brain stem where Sechenov 

 concluded the inhibitory apparatus lay. 



physiology ever since, the theory of conditional re- 

 flexes. 



Sechenov's experiments that proved so crucial to 

 his future thinking were on the effect on reflex move- 

 ments of salt crystals placed at various levels of the 

 transected neuraxis (308). His preparation (309) was 

 the decapitated frog, a toe of which he dipped into 

 acid, a procedure that had been developed by Tiirck. 

 He timed the interval between stimulus and onset of 

 withdrawal of the frog's foot by counting the beats of 

 a metronome. In this way he got some index of the 

 degree to which application of the salt crystal to the 

 brain stem slowed withdrawal. Sechenov interpreted 

 lengthening of withdrawal time as inhibition of reflex 

 activity. The selection of a salt crystal as a stimulus 

 seems strange in the hands of a pupil of du Bois- 

 Reymond's and is reminiscent of Marshall Hall's use 

 of it half a century earlier to study depression and 



308. Sechenov, Ivan Mich.mlovich (1829-1905). Physiolo- 

 gische Studien iiber die Hemmungsmechanismus fur die Re- 

 flexthdiigkeit des Riickenmarks im Gehirne des Frosches. Berlin : 

 Hirschwald, 1863. 



309. Sechenov, I. M. Note sur les moderateurs des mouve- 

 ments reflexes dans le cerveau de la grenouille. Acad. Sc, 

 Paris 1863. 



augmentation of spinal reflexes. Only later (310) did 

 .Sechenov use electrical stimulation in his experiments 

 on the 'spontaneous' variations of spinal cord poten- 

 tials which he regarded as signs of activity in the 

 spinal centers. This was the first experimental ap- 

 proach towards a centrally exerted inhibitory action 

 on skeletal ('voluntary') muscle. 



Although at this stage his own experimental evi- 

 dence seemed slender, Sechenov must have been 

 pondering its meaning in much wider terms, for a 

 year later, on his return to Rus.sia, he published as a 

 series of articles the essay (31 1) that proved to be so 

 influential in Rus.sian physiology. This essay on the 

 Reflexes of the Brain was later (1866) published as a 

 book after a stormy period during which efforts were 

 made to suppress its publication and censure its 

 author. This opposition was stirred by Sechenov's 

 assertion that all higher brain function was a material 

 reflex consisting of three sectors — an afferent initia- 

 tion by sensory inflow, a central process entirely sub- 



310. Sechenov, I. M. Galvanische Erscheinungen an dem 

 Verlangerten Marke des Frosches. Arch. ges. Physiol. 27: 

 524, 1882. 



311. Sechenov, I. M. Reflexes of Ike Brain. Medizinsky Veslnik, 

 1863; English translation in Sechenov's Selected Works. 

 Moscow-Leningrad: State Publ. House, 1935, p. 263. 



