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1. Frequencygrams of rabbit spindle primary endings elicited by stimulation of single fusimotor axons were obtained by the method described by Bessou, Laporte & Pagès (1968a) which gives indirect information on the contraction of intrafusal muscle fibres.
2. Repetitive stimulation of the majority of static axons (twenty out of twenty-five axons studied) gave frequencygrams showing discrete large peaks corresponding to each stimulus, even for rates of stimulation as high as 300-500/sec.
3. Large responses to single stimuli were elicited by thirteen of these axons. The responses consisted of a fast-rising phase lasting 5-10 msec and declining phase lasting 30-50 msec.
4. Repetitive stimulation of some static axons (five out of twenty-five) gave frequencygrams displaying a smooth contour with no sign of individual responses to single stimuli and with a slow rising and declining phase.
5. Both kinds of `static' frequencygrams may be obtained from the same spindle.
6. Repetitive stimulation of dynamic axons gave frequencygrams of small amplitude with a slow rising and declining phase and no sign of individual responses, even at low rates of stimulation.
7. Although rabbit spindles lack nuclear chain muscle fibres (Barker & Hunt, 1964), rabbit's frequencygrams were essentially similar to those of cat spindles. The functional implications of this similarity are discussed.
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