DEMONSTRATIONS. 143 



tendo Achillis. In this arrangement the surface of the tendon is negative to 

 that of the muscle. 



2. On exciting the muscle by faradizing its nerve, a deflection takes place 

 in such a direction as to indicate that the electrical difference between the 

 two surfaces is diminished. After excitation the needle resumes its former 

 position. 



3. The electrode in contact with the tendinous expansion is now brought 

 near to its fellow, so that both contacts are now muscular. They are nearly 

 isoelectrical. On injuring the lower of the two contacts mechanically or by 

 heat, it becomes at once strongly negative. On excitation of the nerve by 

 induced currents, the negativity diminishes as before. 



4- Electromotive Phenomena of the Ventricle of the 



Frog Heart. A Stannius' Heart Preparation (see Practical Exercises) is 

 " led off" by contacts at its apex and base. If the heart is uninjured, these 

 surfaces will be found to be nearly isoelectrical. On injuring either surface it 

 becomes negative. 



2. A normally contracting heart is led off by contacts similarly situated. 

 Each contraction is accompanied by a deflection of the needle, indicating that 

 the apex becomes first positive then negative. By injuring the apex, mechani- 

 cally or otherwise, the deflection becomes entirely positive. 



3. A "ventricle preparation " is led off at apex and cut surface. During 

 contraction, the effect is similar, but the negative deflection is much larger. 



4. A ventricle apex preparation (which does not contract spontaneously) is 

 led off as above. Its cut surface is at first strongly negative to the apex. On 

 excitation at the base by a single induction shock, the ventricle contracts, its 

 contraction being accompanied by a deflection indicating that the apex becomes 

 negative. 



H. K. LEWIS, PRINTER, 136 GOWER STREET, LONDON. 



