212 



Mr. G. J. Romanes on the 



[May 3, 



nervous elements. It is therefore to be expected, upon the theory of 

 electrotonus, that the muscle under these conditions should prove itself 

 most sensitive to the closing excitation when the nerve-trunk rests on 

 the kathode, and most sensitive to the opening excitation when the 

 nerve-trunk rests on the anode. .... 



" If the gastrocnemius of a frog be placed on non-polarizable electrodes 

 in the position just described, and if care has been taken not to injure 

 the attached sciatic nerve, I find that upon now dividing this nerve, either 

 near or just within the muscle, remarkable alterations ensue, not only, as 

 is already known, in the general sensitiveness of the muscle, but also, and 

 more particularly, in "its relative sensitiveness to make and to break of 

 the current. . . . For just as before cutting the normal sensitiveness 

 of the muscle is greatest to the closing excitation when its femoral end 

 (or uninjured nerve-trunk) rests on the kathode, and most sensitive to 

 the opening excitation when this end rests on the anode, so, after the 

 general sensitiveness has been exalted by cutting, the exaltation shows 

 itself in a far higher degree to the closing excitation when the femoral 

 end (or severed nerve-trunk) rests on the kathode, and to the opening 

 excitation when this end rests on the anode." 



Having thus described the qualitative effects of nerve-injury in relation 

 to electrotonus, my former paper went on to describe also the quantitative 

 effects ; but for my present purpose it is unnecessary to quote the latter. 

 For having observed that the particular effects of nerve-injury which I 

 was investigating decreased with great rapidity after the first infliction of 

 the injury, I deemed it desirable to confirm the quantitative results 

 already published by employing a more rapid method of varying the 

 intensity of the voltaic current. Accordingly, instead of using the rheo- 

 chord, I introduced into the exciting circuit a rheostat consisting of a long 

 U-tube charged with dilute solution of zinc sulphate. Into each leg of 

 the TJ-tube there dipped a zinc rod of the same length as the tube. These 

 two rods formed part of the circuit, and as, by means of an appropriate 

 mechanical arrangement which need not be described, they could be slid 

 up and down the legs of the tube with great facility, the resistance 

 offered by the tube could thus be varied w T ith great rapidity. 



In some other respects, also, I changed the method. Instead of non- 

 polarizable electrodes I used platinum plates measuring 4 millims. across. 

 Also, in order to estimate the maximum effect produced by nerve-injury in 

 each of the four cases (<r«), (5), (c), and (d), I only made one comparative ob- 

 servation on every muscle I employed. That is to say, if I wished to ascer- 

 tain the maximum degree in which the excitability of a nerve is increased by 

 section in any one of these four cases, I began by observing, in the unin- 

 jured nerve, the maximum number of Ohm's units of resistance which I 

 could afford to throw into the U-tube, so as only just to procure a 

 response to the make or break stimulus as the case might be. Having 

 noted this, I raised the sliding rods to the top of the U-tube, so as to 



