RESPONSE OF NERVE 719 



has been proved to occasion an erectile movement of the 

 leaf with galvanometric positivity (figs. 44, 45, and 46). The 

 transmission of true excitation, on the other hand, gives rise 

 to a fall of the leaf and the electrical response of galvano- 

 metric negativity. Again, the transmission of excitation in 

 the plant is modified similarly by those varying physiological 

 conditions which influence it in the case of the animal. 

 Thus, a strong stimulus is transmitted more quickly, other 

 things being equal, than a feeble. Fatigue, on the other 

 hand, is found to depress the velocity. The application of 

 cold reduces or temporarily abolishes the transmission, while 

 warmth enhances its velocity. Anaesthetics, again, are found 

 to depress conductivity. And lastly, the polar effect of 

 currents, in the plant as in the animal, is to induce opposite 

 changes, according as anode or kathode is applied. I have, 

 moreover, been able to isolate certain tissues specially fitted 

 for the conduction of excitation. These are found in the 

 soft parts of the fibre-vascular bundles, and are particularly 

 easy to isolate in the case of fern. They here possess the 

 relatively high velocity of about 50 mm. per second. It 

 may be said, in view of their peculiar responsive charac- 

 teristics, and the modifications of their response under given 

 conditions, that these structures are indistinguishable from 

 animal nerves, and may therefore be rightly designated 

 vegetal nerves. On isolation, for example, these highly 

 excitable vegetal nerves, like the animal nerve, when isolated, 

 are liable to fall into a state of sub-tonicity, on account of 

 which their conducting power is temporarily impaired. The 

 transmitted effect of stimulus, then, as in the corresponding 

 case of animal nerve, becomes one of abnormal galvano- 

 metric positivity. Continuous stimulation when in this state, 

 however, by carrying the tissue out of the A into the 

 B condition, converts the abnormal positive response into 

 normal negative, through an intermediate diphasic, in the 

 plant as in the animal nerve. When in the B stage, again, 

 tetanisation has the effect of enhancing response in both. 

 The effects of ether, carbonic acid, alcohol vapour, and 



