CONDUCTIVITY 147 



of dry substances remain. Even of this 25 per cent, by far 

 the largest part is apportioned to connective tissue, for which 15 

 per cent, is certainly not too high a figure. Neither can the re- 

 maining 10 per cent, of dry substances be regarded as consisting 

 entirely of molecules capable of decomposition. For in this is 

 also included the organic reserve material of the axis cylinder pro- 

 toplasm, which is doubtless of very considerable amount. Further, 

 the salts and products of disintegration, for which the estimate 

 for the sum total would probably not be too low if we assume the 

 amount to be equal to that of the group specially concerned in 

 the process of excitation. As, however, a constant metabolism 

 of rest takes place, these last molecules or atom groups are cer- 

 tainly not at the moment of entrance of the stimulus in their 

 entirety in a condition capable of decomposition. It is quite cer- 

 tain, therefore, that we are still overestimating the amount of the 

 molecules capable of disintegration, if we put them down as 5 per 

 cent, of the entire nerve substance. If we now suppose that this 

 5 per cent, of irritable molecules are broken down as a result of 

 stimulation, 95 per cent, of nonirritable substance, separating 

 these irritable molecules, must become heated to such a degree 

 by the disintegration of the latter that the amount of heat suffices 

 to bring about decomposition of the nearest surrounding mole- 

 cules or atom groups, for otherwise conduction of disintegration 

 could not take place in this manner. This condition presents a 

 serious difficulty for the assumption that heat is the form of 

 energy responsible for the conduction of disintegration. It is 

 true that we cannot reject this view at once as being completely 

 incorrect, as the possibility of conduction does not depend upon 

 the absolute amount of heat which reaches the next molecule 

 capable of decomposition, but upon the relative amount of heat 

 in regard to the degree of lability of the irritable molecules, 

 of which we cannot even approximately make an estimate. How- 

 ever, by a comparison with other highly explosive substances, 

 such as iodide of nitrogen, we find that a slight trace of water 

 applied to the iodide of nitrogen suffices to prevent the extension 

 of the disintegration process, and with this the explosion of the 

 whole mass. Nor does the view of Pfliiger remove this difficulty, 



