THE CONDUCTIVITY BALANCE 483 



up-responses were obtained when it was contrariwise too far 

 to the right More careful adjustment reduced this up- 

 movement, as seen in the next two responses, and finally, 

 when the exact balancing-point was reached, the effect was 

 null, as seen in the horizontal record. 



In studying the question of the variation of responsive 

 excitability induced by any given reagent, the agent is 

 applied at the point E to the right. Any variation of excit- 

 ability will then upset the balance. If the reagent be of a 

 stimulatory character we shall obtain a resultant up-response, 

 but if it be of a depressing nature, E will be rendered rela- 

 tively the less excitable of the two points, and the response 

 will consequently be down. It will thus be seen that that 

 upsetting of the balance by which either up- or down-responses 

 are induced is due simply to the relatively excitatory or 

 depressing effect of the reagent, and is completely inde- 

 pendent of any variation of resistance which might be 

 brought about by its application. In the course of the 

 following investigation, it is to be understood that the elec- 

 trical connections are so made that the greater excitation of 

 the right-hand contact is always represented by up-response, 

 and vice versa. If it be desired to make a comparison 

 between the excitatory reactions of two reagents, then the 

 two are applied simultaneously, one at E and the other at E'. 

 The resulting record then affords us a continuous graphic 

 illustration of the relative and varying effects of the two. 



If, again, it is the influence of any agent on conductivity 

 that is to be studied, we first take a balanced record and then 

 apply the given reagent on an area of about I cm. at C on 

 the conducting arm. In this case, the responsive excitabilities 

 of the two points E and E' are the same, but if the effect of 

 the agent have been to induce increased conductivity of C, 

 then the excitation transmitted to the right-hand side, E, will 

 be greater, and the response caused by the upsetting of the 

 balance will be upwards. Conversely, a down-response will 

 indicate that the effect of the agent has been to depress the 

 conductivity. Again, we can compare the relative effects in 



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