66o 



PRINCIPLES OF GENERAL PHYSIOLOGY 



p. 184). The fatigue is simultaneous for direct and indirect stimulation, and is 

 thus situated in the active cells themselves, not in an intermediate substance. 



Experiments on heat production have shown that it is very minute ; but the 

 results are somewhat contradictory, and it has been suggested that two processes 

 may be going on, an endothermic and an exothermic one. Correspondingly, only 



infinitesimal chemical changes have been 

 detected. 



The conclusion seems to be indicated 

 that the process is one involving very 

 slight expenditure of energy, apart from 

 that necessary for the current itself. 

 Probably the chief process is one of change 

 of permeability, involving redistribution of 

 ions. 



The electric fish are relatively insen- 

 sitive to electrical shocks, although not 

 entirely so, as was thought at one time. 

 This state may, perhaps, depend on some 

 peculiarity of the permeability of their cell 

 membranes to ions ; that is, it may be a 

 bad electrolytic conductor, as suggested by 

 Garten (1910, p. 212). 



The, Retina. The significance of the 

 electrical change in this organ has been 

 discussed above (pages 523-524). 



Plant Tissues. In accordance with the 

 general theory of the mode of production 

 of differences of electrical* potential, it 

 would be expected that all phenomena 

 associated with changes in the permeability 

 of the cell membrane would give rise to 

 electrical effects. Owing to the short 

 circuits present in all tissues, it is only 

 when the processes take place with some 

 rapidity that it is possible to detect them. 



Some cases have already been given. 

 Dionsva and the sensitive plant (page 430), 

 the effect of light on the green leaf (page 

 567), and the moving protoplasm of Nitella 

 may be mentioned. 



Loeb and Beutner (1912) and Beutner 

 (1912) made some interesting experiments 

 on the apple. Tf both electrodes are on 

 uninjured surfaces, change of the electro- 

 lyte concentration in one of the electrodes 

 causes the appearance of a potential differ- 

 ence, owing to change of concentration of 

 the ions forming the double layer, and the 

 magnitude of the effect follows the Nernst 

 The addition of non - electrolytes, urea 



h 



FIG. 216. ELECTRICAL ORGAN OF THE 

 SKATK. Microscopic structure of part 

 of one of the discs. Somewhat dia- 

 grammatic. 



a, Transverse septum 



b, Mc'(lull:ii i-d fibres of plexus 



c, Terminal ramifications of non-medul 



late<l nerve fibres 



Nervous 

 lamina. 



\ The (list-. 



d, Nucleated layer 

 f. Striated layer 

 f, Alveolated' ' 



i/. Connective tissue. 



A, Transverse septum at its junction with the longi- 

 tudinal septum ; a nerve is seen in section. 



(Burdon-Sanderson and (inteh, 

 Jl. of rhytnol., 9, p. 143.) 



formula as given above (page 191). 



or sugar, does not affect the potential difference. All cations act in the 

 same way, as was explained above (page 161), owing to the possibility of 



free interchange between ions of the same sign. It may be remarked that 

 interchangeability as regards all cations distinguishes the kind of concentration 

 battery in question from that where metallic electrodes are concerned. In the 

 latter case, of course, it applies only to salts of the particular metallic ion itself. 

 In the former case, the electrode, by interchange, becomes one composed of all 

 the cations present outside it, in corresponding concentrations. 





