CHAPTER XLI 



THE MOLECULAR THEORY OF EXCITATION AND ITS 

 TRANSMISSION 



Two opposite responsive manifestations, negative and positive Such opposite re- 

 sponses induced by polar effects of currents of different signs Arbitrary nature 

 of term ' excitatory ' Pro-excitatory and anti-excitatory agents Molecular 

 distortion under magnetisation in magnetic substances Different forms of re- 

 sponse under magnetic stimulation Mechanical, magneto-metric, and electro- 

 motive responses Uniform magnetic responses Response exhibiting periodic 

 groupings Ineffective stimulus made effective by repetition Response by 

 resistivity- variation Molecular model Response of inorganic substance to 

 electric radiation Effect of rise of temperature in hastening period of re- 

 covery and diminishing amplitude of response Sign of response reversed under 

 feeble stimulation Conduction of magnetic excitation The Magnetic Con- 

 ductivity Balance Effect of A-tonus and K-tonus, on excitability and con- 

 ductivityConducting path fashioned by stimulus Transmission of excitation 

 temporarily blocked in iron wire, as in conducting nerve Artificial nerve- 

 and-muscle preparation. 



IT is admitted that the excitation of living tissues is brought 

 about by some kind of molecular disturbance, and that the 

 passage of this molecular disturbance from point to point is 

 the transmission of excitation. As we do not possess the 

 power of molecular vision we have perforce to be contented 

 with the vagueness of the ideas which these terms connote, 

 complicated as they are by the concomitance of other 

 apparently mysterious properties of living tissues. If re- 

 sponse and its variations, however, be in truth mainly de- 

 pendent on the molecular condition of the tissue and its 

 upset, then, from molecular considerations alone, it must 

 be possible to explain why, under certain conditions, the 

 responding substance is increased in excitability, and under 

 others depressed. It has hitherto been found impossible to 

 determine what is the nature of the antecedent molecular 



