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Mr. Graham Brown. 



contractions, from which the estimation of the number of grades of 

 contraction was made. 



At the end of each experiment a maximal reflex contraction was 

 registered. The remaining motor twig to tenuissimus was then divided, and 

 the same reflex stimulus was again applied. If there was no muscular 

 response it was assumed that that twig contained all the remaining motor 

 fibres, and these were counted after staining with osmic acid. The number 

 of different heights of reflex contraction was then counted and compared 

 with the number of nerve fibres. Differences in height of under 0"5 mm. 

 were neglected, and the heights were measured from the level of contraction 

 which obtained at the commencement of each reflex contraction. 



The following table gives details of six experiments : — 



No. 



Fibres. 



Grades. 



Kind of series. 



1 

 2 

 3 



4 

 5 

 6 



31-33 

 24-27 

 42 



30 

 48 

 28 



i 



27 

 47 

 40 

 54 

 27 



28 ( + 21 ?) 



31 



Ascending series. 

 Descending series. 

 Ascending series. 

 Descending series. 

 Ascending series. 

 Ascending series (broken). 

 Ascending series. 



In Experiment 5 the series was taken in groups. Thus first a group of 10 

 closely graded stimuli was registered. The stimulus was then increased 

 10 times more than the increase between each pair of elements of this 

 group, and a second closely graded group was registered. Again the stimulus 

 was more greatly increased, and a third closely graded group was registered — 

 and so on. As in each group there were about seven different grades amongst 

 the 10 contractions, and as there were three "gaps" it is reasonable to 

 suppose that about 21 grades should be added. The difference in height 

 between the end contraction of a group and the commencing contraction of 

 the next group was nearly the same (being sometimes greater) than that 

 between the initial and terminal contractions of a group. 



It will be observed that there are more grades in a descending series than 

 in an ascending one. If the least favourable kind of series — that is, the 

 ascending — be taken, it is found that the number of grades of reflex con- 

 traction corresponds fairly closely with the number of nerve fibres in the 

 efferent nerve. It is sometimes a few more and sometimes a few less. 



If this be the case, then there are more grades of reflex contraction than 

 there are efferent nerve fibres. 



For, in the first place, the presence of deterioration of the motor response 



