Fractional Activity in Mammalian Reflex Phenomena. 139 



probably means that there should have been more grades than were actually 

 recorded. 



And secondly, not all the fibres in the efferent nerve are efferent nerve 

 fibres. A certain proportion of them are afferent nerve fibres from the 

 sensory end-organs in the muscle. If tenuissimus conforms to the ordinary 

 rule, about two-thirds to one-half only of the fibres in the motor nerve are 

 efferent — for that is the proportion which Sherrington* found for the 

 monkey and cat. 



VI. Conclusions. 



The experiments here described seem to show that the number of different 

 mechanical responses with which a specific individual muscle (a flexor) 

 answers certain reflex stimuli (ipsilateral flexion-producing) of different 

 intensities may be greater than the number of efferent fibres in the motor 

 nerve. The differences in mechanical response are here measured by 

 estimating the extent of the greatest shortening of the muscle during a reflex 

 tetanus which lasts 1 sec. 



On the assumption that each difference in shortening of a greater extent 

 than - 5 mm. in the tracing as magnified by the lever is a measure of a 

 different degree of reflex activity, it would seem that the activity evoked 

 reflexly in the efferent nerve fibres here investigated has not an " all or 

 none " character ; and that the discharge of any efferent neurone may be 

 graded in resonance with graded afferent stimuli. 



But it must be admitted that the mechanical response is a coarse indicator 

 — even under the conditions here used. And it must further be admitted 

 that even if there is a larger number of mechanical responses than is the 

 number of efferent nerve fibres this does not of necesssity exclude the 

 possibility of an " all or none " character in reflex efferent discharges. 



It is possible, for instance, to look upon the efferent part of a system as 

 composed of three longitudinal parts — A, B, and C — each of which consists 

 of efferent neurone and subservient muscle fibres. Three graded afferent 

 stimuli might discharge: the first, A; the second, A + B; the third, 

 A + B + C. In such an arrangement it would be expected that there would 

 be three distinct and separable grades of mechanical response. But it is 

 also possible that a series of graded afferent stimuli might discharge : the 

 first, A ; the second, A + B ; the third, A + (but not B) ; the fourth, B + C 

 (but not A); the fifth, A + B + C. In such a case there would, therefore, 

 be five possible mechanical responses if the muscular elements were of 

 different efficiencies. This is certainly a possibility, but it must appeal to us 

 at present as being too artificial a possibility. 



* ' Journ. Physiol.,' 1894, vol. 17, p. 211. 



L 2 



