Fractional Activity in Mammalian Reflex Phenomena. 135 



Plausible as this objection to the " all or none " character of a certain 

 specific afferent activity seems, it must be remembered that the imperfections 

 of the eye may condition irradiation and halation sufficient to allow of the 

 explanation of the phenomenon on the " all or nothing " principle. 



But again, a wide range of touch sensations of different intensities may 

 be obtained on stimulating the one point on the skin with stimuli of different 

 values — and this even when the area of skin stimulated is supplied by a 

 single afferent nerve. Here there seems to be no " all or none " response to 

 graded stimulation. 



Yet again, Sherrington* found for the scratch-reflex of the spinal dog that 

 a dozen or more grades in the reflex response might be obtained on graded 

 punctiform stimulation of the same skin-point — that is, of the same afferent 

 nerve fibre. 



These two latter observations seem to point very strongly to the conclusion 

 that there must be a grading of the response, at any rate, in certain varieties 

 of afferent nerve fibres of the mammal in reply to graded intensity of 

 stimulation. And when we examine the possibility that the reflex discharge 

 of the efferent neurone is of an " all or none " character certain difficulties 

 are presented. 



In the first place we have Sherrington's - ] - statement that in a reflex 

 response of the muscles of the hind linib of the mammal all the contractors 

 are active in the minimal reaction, and that grading of the intensity of the 

 reaction in response to grading of the intensity of the stimulus is accom- 

 plished by an increase in the activity of each contractor. If, however, the 

 activity of each individual contractor is conditioned by a fractional activity 

 of its fibres, it is, at any rate, strange that the thresholds of the most excitable 

 fractions should be the same in all the contractors. 



Secondly — perhaps not a very grave difficulty — there is the question of 

 " tonus." This slight contraction on the " all or none " theory must be 

 looked upon as due to the activity of a few of the muscle fibres only. But 

 no sagging or wrinkling is seen in parts of a tonically contracted muscle, 

 and the pull of the muscle where the tendon is a broad one is not seen more 

 at one side than another. 



Thirdly — and a more formidable difficulty — the " beats " of the scratch- 

 reflex are usually "incomplete." That is to say, the flexor (for instance) 

 exhibits a series of partial relaxations and reconstitutions of contraction. 

 These may be looked upon as conditioned by a series of incomplete refractory 

 phases. Now under an " all or nothing " theory each partial relaxation must 



* ' Joura. Physiol.,' 1906, vol. 34, p. 1. 

 t ' Journ. Physiol.,' 1910, vol. 40, p. 28. 



