574 THE PHYSIOLOGY OF ELECTRICAL ORGANS. 



applied to the exposed nerve. On the other hand, the organ readily 

 responds to mechanical stimulation of the nerve, even when this is the 

 mere vibration obtained by Uexkiill's nerve-shaker. 



The alteration in the magnitude of the response of the organ to the 

 stimulation of its nerve by induced currents, resembles that of a motor 

 nerve with its nerve-endings rather than that of a muscle. Thus the 

 organ response increases with the augmentation of the exciting cur- 

 rent, through a much larger range than does that of a muscle, whilst 

 the resemblance to nerve-endings is shown by the circumstance that 

 the organ response is diminished by previous activity. It is true that 

 an isolated piece of organ, if kept cool and moist, can be excited several 

 times before there is any very marked diminution in the size of the 

 response ; but such diminution does occur, and has been studied by 

 Schonlein, in torpedo strips repeatedly stimulated by the repeating 

 rheotome ; hence fatigue can be produced, and the organ thus resembles 

 nerve-endings as regards fatigability. 1 It should, however, be remarked 

 that the discharge of the entire organ through the central nervous 

 system becomes far more rapidly weakened, unless ample periods of 

 repose alternate with those of activity ; this is due to central fatigue. 



(d) Influence of arrest of circulation. In close connection with the 

 question of fatigability is the extent of modification which portions of 

 tissues show when kept in the cold and in appropriate moist surround- 

 ings for many hours. Such portions may respond even after thirty-six 

 hours to exciting stimuli, but are far more susceptible to fatigue and 

 are evidently in a condition of lowered excitability. This is shown 

 by the small extent to which the phenomena of self-excitation, to be 

 referred to later on, are now observed. The altered condition of the 

 tissue is further shown in Malapterurus preparations, by the circum- 

 stance that careful analysis of the electrometer record shows the 

 response to be slower in development than is that of the freshly 

 excised organ. In both Torpedo and Malapterurus, portions of kept 

 organ sometimes exhibit a further phenomenon. A rapid series of 

 responses affecting the recording instruments may suddenly be observed 

 in the absence of any obvious stimulus. This often appears to usher in 

 a gradual diminution and final extinction of excitability ; and since the 

 organ is refractory to chemical, but very susceptible to mechanical, 

 stimulation, it is probably due to the nerve-shatter caused by drying, 

 and resembles the familiar muscle tetanus, which is so readily produced 

 by the drying of portions of a motor nerve. 



Influence of such drugs as affect muscles and glands. The 

 comparative indifference of the organ to such drugs as curari and 

 atropin is a remarkable and suggestive fact. Torpedoes can be curarised 

 by placing them in salt water containing the alkaloid, until they are 

 quite immovable, yet, when touched, they give violent shocks, showing 

 that the functional activity of the organ is still at the beck and call of 

 the nervous system. 2 The organ of Malapterurus with its nerve, can be 

 soaked in 1 per cent, curari solution, without undergoing any appreci- 

 able alteration in its susceptibility to respond to nerve excitation. 3 



It has been recently found that when large doses of curari (15 c.c. of 



1 Schonlein, Ztschr. f. BioL, Miinchen, Bd. xxxi.; Bd. xxxiii. S. 408. 



2 Moreau, Ann. d. sc. nat., Paris, 1862, tome xviii. ; Gotch, "Proc. Physiol. Soc.," 1888, 

 p. 6, Journ. Physiol. , Cambridge and London, vol. ix. 



3 Gotch and Burch, loc. cit. 



