Fractional Activity in Mammalian Reflex Phenomena. 141 



VII. Summary. 



The mechanical response of tenuissimus — a flexor in the hind limb of the 

 cat — to graded reflex stimuli (tetani, lasting one second) seems under certain 

 conditions to exhibit grades of difference greater in number than the number 

 of efferent fibres in the motor nerve which supplies it. 



On the assumption that the differences here observed denote differences 

 in the activity of reflex discharges, this seems to show that the discharge of 

 the efferent neurone in a specific type of reflex activity has not the character 

 of an " all or none " response to graded stimuli. 



This does not, of course, exclude the possibility that within the neurone 

 there are units, the activities of which have this character. 



Experiment 24.10.12 (No. 5 in table). Decerebrate cat; a record of the 

 mechanical responses of right tenuissimus obtained in response to graded 

 reflex stimulation of the right great sciatic nerve. Cat decerebrated 

 10.45 A.M. 



The series was started at 11.27 a.m. The reactions are obtained in response 

 to tetani lasting 1 sec. (rate of stimuli 30 per second), and they are taken 

 every minute. The electrical stimuli are graded at first — with the primary 

 and secondary induction coils 150 mm. apart — by rotating the secondary coil 

 and thus diminishing the angle between its axis and that of the primary by 

 1° for each reaction. Later in the series the electrical stimuli are graded by 

 pushing the secondary coil 1 mm. nearer the primary for every reaction (the 

 axes of the coils then are parallel). The series is broken into groups of 10, 

 and between the groups the electrical stimulus was graded tenfold the grading 

 between the elements of the group by 10° or 10 mm. Between the five final 

 reactions the grading is also of this order. Beneath each tenth reaction the 

 value of the evoking stimulus (either in degrees divergence of the secondary 

 axis at 150 mm. distance between coils, or in millimetres distance of coils 

 with axes in line) is recorded. 



In the first group there are at least eight different mechanical grades. 



In the second group there are at least seven different mechanical grades. 



In the third group there are at least seven different mechanical grades. 



In the fourth group there are at least five different mechanical grades. 



For the fifth group at least two more grades may be added. This gives 

 a total of at least 29 mechanical grades. It can hardly be doubted that about 

 the same proportion of grades would have been present in the first three 

 intervals. On the assumption that in each of these there were seven distinct 

 grades the total number of grades for the series would be about 50. " Quick " 

 series registered before and after this record showed deterioration. This 



