27O COMPARATIVE ELECTRO-PHYSIOLOGY 



Du Bois-Reymond, as, in reality, a persistent after-effect of 

 excitation, gathers confirmation from an observation made 

 by Gotch, that it is considerable in Torpedo, in which the 

 excitatory effect also is known to be very persistent ; but in 

 Malepterurus, where recovery from excitation is rapid, this 

 particular organ-current is practically absent from excised 

 preparations. 



We may turn now to the repeated or oscillatory character 

 observed in the electrical discharge by both Gotch and 

 Schonlein. This is seen in the multiple apices of its 

 rheotomic curve. Multiple apices are also found, as we have 

 seen, in the rheotomic observations on vegetable organs, 

 given in fig. 40. Gotch attempts to explain these repeated 

 responses of the electrical organ which he calls 'auto- 

 excitation 'by the passage through the tissue of the intense 

 current due to the response ; this he regards as exciting the 

 tissue again, and bringing about the repetition of the same 

 effect. With regard to this hypothesis, however, it is un- 

 necessary to suppose that it is the intense electrical current 

 of the first response which is the exciting cause of the 

 second, and so on. For we must bear in mind that multiple 

 response is not exclusively characteristic of these electrical 

 organs, with their high intensity of discharge-current, but 

 is exhibited by tissues of various kinds. These, as we have 

 seen in Chapter XVII., may be thrown into a condition of 

 rhythmic or multiple excitation by any form of stimulus, 

 provided that its intensity be beyond a certain value. It thus 

 happens, as we have seen, that while a single moderate stimulus 

 induces a single response, a single strong stimulus induces 

 multiple responses. 



Indeed this fact that it is not the intensity of the 

 first responsive current, causing a new excitation of the 

 tissue, which is accountable for the second, and so on 

 becomes quite clear, as soon as we make quantitative obser- 

 vations of response, in those cases in which it receives 

 undoubted visible manifestation, by the orderly fall of leaflets 

 serially arranged that is to say, in such plants as Biophytum, 



