STIMULI AND THEIR ACTIONS 427 



branches drop at once and the leaves flap together in the typical 

 manner. 



Other forms of energy are also made manifest by galvanic 

 stimuli. Thus, exact thermo-electric measurements have shown 

 that the temperature of muscle rises in activity, although very 

 slightly, and that, in general, the production of heat stands in 

 inverse proportion to the performance of work. 



That electricity is also produced in the contraction of muscle 

 caused by galvanic stimulation is already clear from our previous 

 knowledge ; an electric tension appears between every contracted 

 point and every resting point, the former being negative to the 

 latter. When, therefore, a contraction-wave runs over the muscle 

 from one end to the other, an action-current can be led off 

 from the two ends at the moment when the wave begins, since, 

 while the one end is contracting, the other is at rest. 



Light also can be produced by galvanic stimulation in pelagic 

 phosphorescent animals, such as Radiolaria and Noctilucw. 



It is evident from our previous considerations that all this 

 evolution of energy in its various forms must be combined with an 

 excitation of metabolism ; it is chiefly the much-investigated 

 muscle that has shown this. The muscle excited to constant 

 activity by stimulation of any sort consumes more oxygen than 

 the resting muscle, it consumes the glycogen stored in it, it produces 

 more carbonic acid than the resting muscle, and, in place of the 

 neutral or alkaline reaction of the latter, it shows an acid reaction. 

 All these changes show very clearly that in muscle when put into 

 activity by stimuli a considerable augmentation of metabolism 

 takes place. 



h. The Phenomena of Depression 



In electrical stimulation also the depression-effects are wholly 

 subordinate in comparison with the phenomena of excitation, and, 

 while the latter have been investigated extensively and carefully, 

 the former are little known. Nevertheless, there appear to be 

 cases in which the galvanic current, especially through long in- 

 fluence or great intensity, is able to produce phenomena of 

 depression. Whether the diminution of the irritability of the 

 nerve that takes place at the anode upon the making of strong 

 currents and at the kathode upon the breaking, and can lead to 

 complete loss of the power of conduction at the place in question 

 without any real destruction, is to be regarded as a phenomenon 

 of depression is more than doubtful ; more extended experiments 

 especially directed to this point are needed. But apparently 

 genuine depressing effects of the galvanic current have been 

 discovered with regard to ciliary motion by Engelmann (79, l)and 

 Kraft ('90). 



