POLARIS A TION PHENOMENA. 587 



excitation. The present writer, working with strips of Malapterurus 

 organ, in 1894, convinced himself that if the strip was narcotised or 

 otherwise altered, so that the excitatory response failed, no homodromous 

 after-effect occurred on the cessation of the homodromous polarising 

 current. Indeed, even in perfectly excitable strips of Torpedo organ, 

 it is possible to do away with the homodromous after-effect by very 

 simple means. For if the polarising current is not too strong (maximum, 

 7 Groves), although a short closure of -005 sec. to '01 sec. is succeeded by 

 an homodromous after-effect, due to the excitatory response overpower- 

 ing negative polarisation effects, yet, on lengthening the period of 

 closure to 1 sec., the negative polarisation is sufficiently increased to 

 swamp the excitatory change, and the usual heterodromous after-effect 

 appears. This will be made clear by the above example. 



The failure to recognise excitation phenomena involved du Bois- 

 Eeymond in a further unwarrantable statement, namely, that the 

 electrical conductivity of an organ strip was very much less for homo- 

 dromous than for heterodromous currents. The evidence for such 

 irreciprocal resistance is quite as unconvincing. Many of the observa- 

 tions were made with induced currents, which were allowed to traverse 

 both the organ and an appropriately arranged galvanometer. If this 

 current was homodromous, the galvanometric deflection was large ; if 

 heterodromous, small; but rheotome observations have shown that, 

 under these circumstances, the former large galvanometric effect was 

 due to the summed effect of the homodromous induced current and the 

 homodromous excitatory response, whilst the small effect was the 

 algebraic sum of the dissimilar heterodromous induced current with the 

 homodromous response. In regard to the observations with voltaic 

 currents of long duration, such interference of the excitatory effect is 

 not so obvious. The subject has been reinvestigated by Schonlein, who 

 used Kirchhoff's well-known methods for estimating electrical resistance 

 and Kohlrausch's bridge. 1 He found that when a current of from 

 20 Daniells or more was led through the excised organ for 30 sees, in either 

 direction, the tissue lost its excitability, and did not respond to ordinary 

 excitation. Accompanying this failure is a diminution of the living 

 electrical resistance. When such currents were led through the tissue 

 for only 01 sec., the tissue showed most irregular results. At one time 

 the homodromous, at another the heterodromous, appeared to have the 

 advantage. There is thus no evidence of such marked irreciprocal 

 resistance as du Bois-Keymond imagined to exist, an irreciprocity so 

 great as only to be accounted for, in his opinion, by assuming an elec- 

 tromotive force of over 30 volts, due to a particular arrangement of 

 those hypothetical molecules with which his name is identified. 



The refutation of positive polarisation and of marked irreciprocal 

 conductivity may seem a matter of small moment, but as their existence 

 was considered by du Bois-Eeyinond as almost a demonstratio ad oculos 

 of the existence of those special electromotive molecules which form the 

 basis of his theory, it is really of some little importance. It cannot be 

 said that the great electro-physiologist contributed much towards the 

 elucidation of the functional activity of electrical organs, and it was the 

 error of ignoring the true excitatory response which appears to have 

 barred his progress. The phenomena of electrical organs may seem 

 somewhat inexplicable, on any present conception as to the source of 



1 Ztschr.f. BioL, Munchen, Bd. xxxiii. S. 408. 



