THE SO-CALLED CURRENT OF REST 571 



definite portion of tissue when excited by means of an efferent nerve. 

 The characteristics of muscle activity have been ascertained by noting and 

 recording the changes occurring in isolated nerve-muscle preparations ; 

 so also those of the electrical organ are best determined by investi- 

 gating the response in isolated nerve-organ preparations. The changes 

 which such a preparation undergoes when its nerve is excited, being 

 entirely electrical in character, have to be studied and recorded by 

 appropriate instruments. Such records must form the basis of our 

 knowledge as to the functional activity of the organ when wielded by 

 the living fish, and the study of the nerve-organ response thus has 

 the same importance as that of the contractile process in a muscle. 



The electrical changes of nerve-organ preparations; activity 

 effects.— It has already been stated that, when a portion of the elec- 

 trical organ with its nerves is cut away from a recently killed Torpedo, 

 Malcvpterurus, or skate, such a portion responds to excitation of its nerves 

 by the development of the intense electromotive change, for the produc- 

 tion of which the tissue is differentiated. In the case of Torpedo, the 

 excised organ may be further separated by incisions running from the 

 dorsal to the ventral surface, and a block thus made containing in its 

 interior a number of entire and uninjured columns. If the nerve 

 entering this mass be carefully dissected out, so that its columnar 

 attachments remain intact, a suitable nerve organ preparation is 

 obtained for the investigation of the response. The ends of the strip 

 may be left covered by their portions of dorsal and ventral skin respect- 

 ively, and brought into connection with a galvanometer, capillary 

 electrometer, telephone, or rheoscopic muscle-nerve preparation. 



In an organ preparation, connected with one of these instruments, it 

 is seen that each single stimulus of the nerve evokes an intense elec- 

 trical response of short duration, the electromotive change being such 

 that a current flows through the organ columns from the ventral to the 

 dorsal skin. 



The response is evoked with each excitation of the nerve by an 

 electrical stimulus, whether an induced or galvanic current, provided 

 this is of sufficient intensity ; it is also evoked with great ease by even 

 slight mechanical disturbance of the nerve, but is not readily caused by 

 those chemical agents (NaCl, etc.) which so easily excite muscular 

 nerves, 1 although it can be produced by ammonia. 



The so-called current of rest. — When connected with a galvano- 

 meter, the piece of Torpedo organ constituting the preparation generally 

 shows a resting electromotive difference, the dorsal surface being galvano- 

 metrically positive to the ventral. A persistent current under these 

 circumstances must be flowing through the excised organ from its 

 ventral to its dorsal surface, i.e., in the same direction as that due to 

 the excitatory response ; it was termed by du Bois-Eeymond the organ 

 current. The theoretical importance attached by du Bois-Eeymond bo 

 the existence of such resting electromotive changes, led him to make 

 an extended series of observations on their character. 2 It appears, 

 however, that the fundamental fact of the existence of this resting 

 difference in uninjured resting organ is problematical. 



In an entire Torpedo, when quiescent, the difference between the 



1 Schonlein, Zischr. f. Biol, Miinchen, Bd. xxxi. S. 161 ; also Cotoli and Burch, Phil. 

 Trans., London, 1896, vol. clxxxvii. 1>, p. 370. 



2 du Bois-Keymond, lor. cit. 



