HITTERS TETANUS. 



203 



details of the law. Instead of reversing the commutator after 

 testing the effect of an alteration of the direction of the current, 

 the student may use one preparation to test at intervals the 

 effect of weak, medium, and strong currents, when the current is 

 ascending, and a second preparation to test the results with 

 currents of varying intensity when the current is descending. 

 The results may be tabulated as follows : R, = rest ; C = con- 

 traction. 



3. Ritter's Tetanus. 



(a.) Connect three Daniell's cells with non-polarisable 

 electrodes short-circuiting with a du Bois key. Prepare a 

 nerve-muscle preparation, and apply the electrode to the 

 nerve so that the + pole is next the muscle i.e., the 

 current is ascending in the nerve. Allow the current to 

 circulate in the nerve for some time (usually about five 

 minutes is sufficient), no contraction takes place. Short- 

 circuit, and observe that the muscle becomes tetanic. 



(b.) Divide the nerve between the electrodes, and the 

 tetanus does not cease ; but on dividing it between the + 

 pole and the muscle, the tetanus ceases. Therefore the 

 tetanus is due to some condition at the positive pole. 



