XV. Demonstration: Electrotonus; to determine the effect 

 of a constant current upon the irritability of a nerve. 



At the beginning of this century Ritter discovered that 

 the vital properties of irritable and contractile tissues 

 were modified when subjected to a constant battery cur- 

 rent. This modified condition was called galvanismus. 

 During the first half of this century the subject was in- 

 vestigated by Nobili, Mattencci, Valentin and Du Bois- 

 Reymond ; the last named substituted the word electro- 

 tonus for galvanismus and further modified the terminology. 

 It remained for Pfluger (Untersuchungen iiber die Physio- 

 logie des Electrotonus, Berlin, 1859) to rework the whole 

 field, to correct, to elaborate, and finally to formulate laws. 

 a. Preliminary experiment. 



1. Appliances. Muscle-signal; 2 Du Bois-Reymond keys; 

 2 Daniell cells ; commutator ; 8 wires ; salt. 



2. Preparation. Set up electrical apparatus as shown in 

 PI. II. Fig. 8. 



j. Operation. Make and mount in the muscle signal a 



gastrocnemius preparation. 

 4.. Observations. 



(1) In which position must the bridge of the commuta- 

 tor stand to give a descending current? Mark that 

 side of the commutator D. Mark the opposite side A. 



(2) With a descending current, which pole is the 

 kathode, a or b? 



(3) PI. II. Fig. 8-p represents the glass plate of the 

 muscle signal. So arrange the triangular platinum 

 electrodes that there shall be a distance of about 1 

 cm. between the electrodes, and both electrodes near 



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