MESSRS. A. WALLER AND A. DE WATTEVILLE ON THE INFLUENCE 
This table shows that alterations of excitability increase with the strength of the 
polarising or pre-existing current, and justifies the statement that:— The greater the 
density of pre-existing current, the smaller the increase of density, and the greater the 
decrease of density necessary to effect stimulus. 
Tracings 35 and 36 illustrate the statement that :— The greater the density of pre¬ 
existing current, the greater the excitatory effect of a given increase of density, the less 
the excitatory effect of a given diminution of density. 
III. Polar Alterations of Excitability tested by Mechanical Excitation. 
In order to ensure the coincidence of excitation with polar alteration of excitability, 
we used the electrode itself as the medium of mechanical excitation. We have found 
only one point of the body which lends itself to the mechanical excitation of nerve, 
viz., the elbow, at the place where the ulnar nerve runs immediately under the skin 
upon a resisting bony groove. Here it is possible, though not always easy, to elicit 
regular contractions by striking a small electrode held steadily over the nerve, with 
gentle and regular blows of an ordinary hammer. The test may appear a rough one, 
but the results are sufficiently uniform and evident to leave no doubt of the reality of 
the alterations. 
When the kathode rests on the nerve, the polar region being therefore kathodic, the 
effect of mechanical excitation is increased; 'when the anode rests on the nerve, the 
polar region being therefore anodic , the effect of mechanical excitation is diminished or 
abolished. 
On breaking the current the contractions appear in both cases greater than before. 
A possible objection must be forestalled. It might be said that the increased effect 
during the kathodic current, is partly due to the change of density in the current, 
arising from the sudden compression of the tissues lying between the electrode and 
the nerve. This is not consistent with the fact that such a change of density would 
increase the contractions when a strong polarising anode is applied, whereas the 
contrary is observed. We may also remark that the effects are equally well observed 
with a large additional resistance in circuit. 
IV. Polar Alterations of Excitability Subsequent to the Passage of the 
Galvanic Current.* 
Preliminary, —Before drawing conclusions as to the state of excitability after the 
passage of the galvanic current, it is necessary to realise the possible influence of 
polarisation currents and alterations of resistance upon the current-strength. 
* The after-effects have been alluded to by some of the authors quoted above (Eulinburg, Samt). 
They form the subject of a laborious inquiry by Remak (“ Ueber Modificirende Wirkungen Galvanischer 
