THEOKY OF THE BREAK-CONTKACTION. 61 



both make- and break-contractions failed to appear even when the 

 slider stood at iooo mm from the zero point 1 . 



If the break-contraction is determined by a polarisation of the 

 nerve, then, ceteris paribus, the susceptibility of the plexus to 

 polarisation must be greater than that of the lower tracts of the 

 nerve. 



And this is actually the case. In experiments on this question 

 the two sciatics of one and the same frog- were fastened together, 

 and different tracts of the nerve submitted to the polarising current. 

 As the same electrodes and the same parts of them were used in all 

 the experiments, and as at the same time the distance between 

 them was constant, it is clear that the differences in the extent 

 of the deflections, which were produced when different parts of the 

 nerve were experimented on, are entirely dependent on local con- 

 ditions. In other words, the polarisability of a nerve differs at 

 different points of its course. What this depends on does not affect 

 the question before us, which is whether any parallelism exists 

 between polarisability and Griitzner's results. I proceed to give 

 some examples of experiments. I examined the polarisation of 

 each nerve preparation at three different places, namely,, (i) at the 

 plexus, (3) where the branches to the thigh were given off, (3) in 

 the lowest part of the nerve. 



Experiment IX. 3 Meidingers, rheochord 1000 ; duration of 

 closure 5"; distance between the electrodes 8 mm . 



I. 



No. Deflection. 



1 2-6 



2 2-95 



3 3-0 



4 2-95 



5 3-0 



Mean ... ... 2.94 



Mean variation 0-056. 



II. 



No. Deflection. 



6 LI 



7 ... i-o 



8 1-25 



9 1-25 



10 1-20 



Mean 1-16 



Mean variation 0-088. 



1 Grutzner, loc. cit. pp. 163-165. 



