526 



PRACTICAL PHYSIOLOGY 



results observed with the make and break of both ascending and 

 descending currents. There is a contraction in each case, but the 

 contraction at break is minimal for the disappearance of anelectrotonus 

 is the less effective stimulus (Fig. 205 (3), (4)). 



The rheochord is removed and the entire current of one or two 

 Daniell batteries is used. There is now a maximal contraction at make 



FIG. 205. Pfltiger's Law of Contraction. 1 and 2, Weak constant current. 3 and 

 4, Moderate strength of current. 5, Strong current. M= point at which current was 

 made, B = point at which current was broken. The numbers 5, 6, 10, and 12 indicate 

 the scale of the rheochord ; 4 D indicates that the current was that of 4 Daniell cells. 

 The arrows indicate the direction of the current, ascending or descending as the case 

 may be. The curve should be read from left to right. (M.S. P.) 



of the descending current, and at break of the ascending current 

 (Fig. 205 (5)). When the ascending current is made the excitation at 

 the kathode is blocked by the anode below ; when the descending current 

 is broken the excitation due to the disappearance of anelectrotonus is 

 blocked by the diminished conductivity and excitability of the region 

 below, in which the katelectrotonus has disappeared. To every action 

 there is a reaction. 



With four or five Daniell cells the experiment is again repeated. The 



