VII. Demonstration: To send an electric current into 

 a nerve gradually. FleischPs rheonom. 



When one studies the effects of thermal, mechanical or 

 chemical stimuli, he may apply the mechanical stimulus so 

 slowly that the nerve may be severed without calling forth 

 a response; he may apply heat to the fresh nerve so grad- 

 ually that the nerve may be actually cooked without caus- 

 ing a contraction of the muscle which it supplies. 



The problem which we have next to solve is to apply 

 an electrical stimulus gradually. 



/. Appliances. Fleischl's Rheonom; 1 Daniell cell; Du 

 Bois-Reymond's "Muscle Telegraph;" contact key; 

 detector; saturated solution of zinc sulphate; 5 wires; 

 frog; operating case. 



The rheonom is constructed as shown in PI. II. 

 Fig. 3 R. Its essential features are: g, the non- 

 conducting base with circular groove; s, the non- 

 conducting rotatable, central standard; P, the battery 

 binding postF, having zinc connection with the groove; 

 p, the rotating, binding posts, having zinc limbs con- 

 necting with the groove. 



2. Experiments and Observations. Set up apparatus as 

 shown in PL II. Fig. 3, after amalgamating the zinc 

 tips which dip into the zinc sulphate. Fill the groove 

 with zinc sulphate. 



(1) Find and mark the zero position for the rotating 

 limbs of the rheonom; i. e., find the position which 

 will give no deviation of the detector needle when 

 the contact key is closed. 



48 



