10 



Mr. G. J. K/Omanes on the 



[May 4, 



which is intended to represent, in a graphic form, the numerical re- 

 lations set forth in the above Table. In each couplet contained in that 

 diagram the left-hand line represents the sensitiveness of the muscle 

 to the stimulus indicated before cutting, while the right-hand line re- 

 presents the sensitiveness of the muscle to the same stimulus after cutting. 

 As in the Table, so in the diagram, all the proportions are referred to the 

 ascending break as to a unit — this being the stimulus to which the 

 muscle is least sensitive, and for which, therefore, the strongest current 

 i s required in order to elicit a contraction. 



"With regard to these results, I may offer the following observations. 

 In the first place, it is evident that the increase of excitability shown by 

 the muscle after cutting is affected to an extraordinary extent by the 

 direction of the current ; and, further, that the manner in which it is so 

 affected is very instructive when considered in relation to the known facts 

 of electrotonus. For just as before cutting the normal sensitiveness of the 

 muscle is greatest to the closing excitation when its femoral end (or nerve- 

 trunk) rests on the kathode, and 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. 

 Thus it is that the curves in figs. 2 and 3 are so much steeper than those in 

 figs. 1 and 4. The only fact, then, that does not seem to admit of any very 

 satisfactory explanation is the altogether dis]pro^ortionate increase of ex- 

 citability which the muscle after cutting exhibits to the descending 

 break (fig. 3) as compared with the ascending make (fig. 2). This fact, 

 therefore, led to the following experiments, 



§ 3. Dr. Burden Sanderson suggested that if we suppose the breaking 

 excitation to be of a more instantaneous nature than the making one, the 

 fact in question might admit of a probable explanation ; for in this case 

 the breaking stimulus would bear more resemblance to an induction- 

 shock than would the making stimulus ; and as it is well known how sen- 

 sitive nerve is to the induction-shock, we might reasonably conclude that, 

 when the sensitiveness of the nerve is increased by section, it would 



in E being high as compared with that in C, the principal part of the current takes the 

 course x, y, C, A. But if a plug be removed from C, the resistance in C is increased* 

 and a proportional amount of the c\irrent takes the direction x, z, E, A. Hence the 

 effect of removing a plug from B is that of diminishing the current in E, vrhile the op- 

 posite effect results on removing a plug from C. 



Such being the apparatus, in all my experiments I removed one plug from B, and 

 thus worked with a current of constant intensity so far as the whole circuit was con- 

 cerned. The requisite variations in the intensity of the stimuli were, of course, effected 

 by the rheochord C. Now the numbers in the above Table are obtained by a very 

 simple calculation. Suppose, for instance, that the minimal ascending break contraction 

 requires 18 ohms' resistance to be thrown into the rheochord, while the minimal ascending 

 make only requires '5 to be thrown in, then the relative sensitiveness of the muscle to the 

 ascending break and make would be approximately represented by the numbers 1 : 36. 



