+-------------------+-----------+----------+ | | | Current | | | Permanent | of | | | Current | Response | +-------------------+-----------+----------+ |B treated with | | | |sodium carbonate. | --> | --> | +-------------------+-----------+----------+ |B treated with | | | |oxalic acid | --> | <-- | +-------------------+-----------+----------+ |B treated with very| | | |dilute potash | --> | --> | +-------------------+-----------+----------+ |B treated with | | | |strong potash | --> | <-- | +-------------------+-----------+----------+ Current of response is always towards the more excitable point. (_a_) Response when B is treated with sodium carbonate.--An apparent positive variation. (_b_) Response when B is treated with oxalic acid.--An apparent negative variation. (_c_) Response when B is treated with very dilute potash.--Positive variation. (_d_) Response when B is treated with strong potash.--Negative variation. The response is up when B is more excitable, and down when A is more excitable. Lines thus ------ indicate deflection due to permanent current.] We have thus seen that we may obtain response (1) by block method, (2) by the method of injury, or relative depression of responsiveness of one contact, and (3) by the method of relative exaltation of responsiveness of one contact. In all these cases alike we obtain a consistent action current, which in tin is normally positive, or towards the relatively more excited. FOOTNOTES: [14] Following another line of inquiry I obtained response to electric stimulus in inorganic substances using the method of conductivity variation (see 'De la Generalite des Phenomenes Moleculaires Produits par l'Electricite sur la Matiere Inorganique et sur la Matiere Vivante,' _Travaux du Congres International de Physique, Paris, 1900_; and also 'On Similarities of Effect of Electric Stimulus on Inorganic and Living Substances,' _British Association 1900_. See _Electrician_). To bring out the parallelism in all details between the inorganic and living response, I have in the following chapters used the method of electro-motive variation employed by physiologists. [15] By 'tin' is meant an alloy of tin and lead used as electric fuse. CHAPTER XI INORGANIC RESPONSE--MODIFIED APPARATUS TO EXHIBIT RESPONSE IN METALS Conditions of obtaining quantitative measurements--Modification of the block method--Vibration cell--Application of stimulus--Graduation of the intensity of stimulus--Considerations showing that electric response is due to molecular disturbance--Test experiment--Molecular voltaic cell.