130 THE SIGNS OF LIFE [LECT. 



ever omitted to control the result observed on the living thing 

 by the identical test applied to the same thing killed. 



77. Fallacies. Fallacy of the electrodes arises from 

 polarisation ; our " unpolarisable " electrodes are not abso- 

 lutely unpolarisable, and may accidentally be quite sensibly 

 polarisable. Their polarisation currents, anomalous or positive, 

 as well as normal or negative, are most manifest with a constant 

 current, much less so, but still sensibly so, with induced currents. 

 We have made use of induced currents only, and shall therefore 

 restrict our attention to these. 



With single shocks I do not think there is any liability to 

 fallacy ; an unequivocal or homodrome blaze-current cannot be 

 simulated by anomalous polarisation, which is a rare and feeble 

 effect manifested by a defective electrode, and quite absent 

 from a properly prepared electrode. An equivocal or anti- 

 drome blaze-current might at first sight be taken as being due 

 to ordinary polarisation, since it is of the same direction ; but the 

 magnitude of the response, its absence from the electrodes 

 themselves when joined, and from the tissue itself when killed, 

 will leave us in no doubt as to the physiological character of the 

 reaction. It is only in the cases where single shocks having 

 proved to be ineffective, we have recourse to the further test 

 of tetanisation by alternating currents, in order to bring out a 

 summated effect (p. 68), that there is any real possibility of 

 deception. Distinguish between the two cases: (i) that in 

 which the alternating currents are passed through the galvano- 

 meter and test-object ; (2) that in which they are passed through 

 the test object only while the galvanometer is short-circuited. 

 The first of these two dispositions reproduces an arrangement 

 that was first adopted by V. Fleischl in the case of nerve, and 

 that I have already considered at some length in that connec- 

 tion. The opposed make-and-break currents are supposed to 

 neutralise each other through the galvanometer, and such deflec- 

 tion as occurs is attributed to an electro-motive action of the 

 test-object. This deflection occurs in the direction of the break 

 current, i.e., is such as would be produced by a physiological 

 reaction in that direction, or as a physical reaction the sum 



