THE MOLECULAR RESPONSIVENESS OF MATTER 



Before f After 



FIG. 10. Abolition of Response in 

 metal by Oxalic Acid 



by vibrating it as a whole, a resultant response will occur. 

 But by the application of oxalic acid to one contact, a resting 

 or permanent current has been induced in the circuit. The 

 responsive or action current 

 originated under stimulation 

 is now found to flow in a 

 direction opposite to that of 

 this resting current that is 

 to say, it causes a negative 

 variation of it (fig. n). 

 The method of response 

 by the so-called negative 

 variation, which is generally 

 employed in studying re- 

 sponsive phenomena in 

 animal tissues, is in reality, 

 as will be seen later, a form 

 of this method of relative 

 depression. 



Various means have been described, in the course of this 

 chapter, for the detection and record of that excitatory change 

 which is brought about by the upsetting of molecular equi- 

 librium under stimulus, 

 and the subsequent re- 

 covery. The responsive 

 change may find expres- 

 sion in different ways. 

 This expression may, 

 for instance, in the case 

 of living tissues, take the 

 form of mechanical con- 

 traction, or of the elec- 

 trical variation of gal- 

 vanometric negativity. 



Or the opposite change, expressed mechanically as ex- 

 pansion, will be evidenced by galvanometric positivity. But 

 it must be borne in mind that neither of these expressions 



FIG. ii. Response by Method of Relative 

 Depression 



f represents current of rest ; 4, represents 

 the action current. 



