GENERAL PHYSIOLOGY OF MUSCLE AND NERVE TISSUE 61 



XVI. ELECTROTONUS (TO DETERMINE THE EFFECT OF A 



CONSTANT CURRENT UPON THE IRRITABILITY 



OF A NERVE). 



At the beginning of the last century Hitter discovered that the 

 vital properties of irritable and contractile tissues were modified 

 when subject to a constant battery current. The modified con- 

 dition was called galvanismus. During the first half of the last 

 century the subject was investigated 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 Pfliiger 1 to rework the whole field, to correct, to elabo- 

 rate, and finally to formulate laws. 



(a) Preliminary Experiment. 



1. Appliances. Muscle signal, or myograph; two Du Bois- 

 Reymond keys; two Daniell cells; commutator; eight wires; salt. 



2. Preparation. Set up electric apparatus as shown in Fig. 37. 



3. Operation. Make and mount in the muscle signal a gastroc- 

 nemius preparation. 



FIG. 37 



4. Observations. (1) In which position must the bridge of the 

 commutator stand to give a descending current so that the cathode 

 will be nearer to the muscle than is the anode? Mark the opposite 

 side A. 



(2) Fig. 37, P, represents the glass plate of the muscle signal. 

 So arrange the triangular platinum electrodes that there shall be a 

 distance of about 3 cm. between the electrodes and both electrodes 

 near that end of the plate farthest from the muscle. Lay the 

 nerve over the electrodes and along the glass plate. The segment 

 of nerve which lies upon the glass plate between the electrodes and 

 the muscle must be subject to various stimuli, mechanical and 

 chemical. At a point about 1 cm. from the electrodes, marked X in 

 the figure, place upon the nerve trunk as many fine crystals of 

 common salt as would be taken up on the point of a penknife. 

 Moisten these salt crystals with a drop of water. While the salt 



1 Untersuchungen Uber die Physiologic des Electrotonus, Berlin, 1859. 



