OF THE GALVANIC CURRENT ON THE MOTOR NERVES OF MAN. 
975 
We also observe that at the termination of an ascending series a weaker current 
than the original current will cause a greater contraction than at first; that at the 
termination of a descending series a stronger current than the original current will 
cause a smaller contraction than at first. These facts indicate in the former case 
diminution of increased excitability, in the latter case a summation of diminished 
excitability which however very rapidly gives way to increase. 
We notice that, cceteris paribus, ascending series are most frequently observed at 
the beginning of experiments (independently of any increase of current strength), that 
descending are most frequently observed after the nerve has been for some time sub¬ 
jected to experiment. This probably signifies that increased excitability is more 
apparent before the general excitability has been raised, diminished excitability while 
the general excitability is raised above normal, and we shall give an observation to 
show that the excitability is raised above the normal, and so remains for a considerable 
period after polarisation (Tracing 32). 
We observe finally that anodic opening contractions at first increase, then gradually 
diminish, and that it requires far stronger or more prolonged currents to produce the 
opening contraction at the end than at the beginning of the experiment. 
Tracing A, 
Series of anodic closure and opening contractions by 150 cells (17 milli webers), 9000 ohms 
additional resistance in circuit. The interruptions in the tracing represent periods of about 
minutes each during which the opening contractions gradually diminished. 
Amidst complex conditions of time, current-strength, and excitability, various 
results are naturally to be expected, and it is to be borne in mind that gradual 
alterations of current-strength, by alteration of resistance and by polarisation currents, 
will adulterate the developing changes of excitability (vide pp. 980, 981). On this 
account we had recourse to the introduction of a considerable additional resistance 
in order to dilute the effects of physical change, and to disengage, as far as possible, 
physiological changes from the physical adulteration. All things considered, we con¬ 
cluded that a descending series, with an excitation rhythm, which previously gave a 
horizontal series, signifies decreasing excitability; that, conversely, an ascending series 
indicates increasing excitability; declining excitability is proved a fortiori when, with 
constant current-strength and excitation rhythm, a previously ascending series is con- 
MDCCCLXXXII. 6 I 
