ADVANCED EXPERIMENTAL PHYSIOLOGY 



325 



STRENGTH OF 

 CURRENT. 



PFLUGER'S LAW OF CONTRACTION. 



DIRECTION OP CURRENT. 



ASCENDING. 



Weak. 



Moderate. 



Strong. 



Very strong 

 and prolonged. 



DESCENDING. 



Make. 



Minimal 

 contraction. 



Maximal 

 contraction. 



Maximal 

 contraction. 



Break. 



No 



contraction. 



Minimal 

 contraction. 



No 



contraction. 



Maximal No 



contraction, contraction. 



FIG. 203. PflUger's Law of Contraction. 



Hitter's tetanus is due to a prolonged excitation at the anode, when 

 the circuit of a very strong current is broken : injury of the anodic 

 region of the nerve abolishes this effect. 



In order to prove Pfl tiger's Law the following experiment should be 

 made. A pair of unpolarisable electrodes are connected to a rheochord 

 by means of a Pohl's reverser 

 in the manner shown by the 

 diagram (Fig. 204). From the 

 Daniell battery two wires pass to 

 the terminals of the rheochord. 

 A muscle- and nerve-preparation 

 is made and is placed in a moist 

 chamber. The lever connected 

 with the muscle is made to write 

 upon a stationary drum. 



By closing a mercury-key a 

 weak current is sent through the 

 nerve in an ascending direction, 

 the anode being the nearer to 

 the muscle. A minimal contrac- 

 tion occurs at make, but there is 



no contraction at break, for the rise in excitability at the former 

 anode is insufficient to cause an excitation (Fig. 205 (1), (2)). The 

 current is reversed and the experiment is repeated. 



Now by means of the rheochord the current is strengthened and the 



FIG. 204. Diagram of the experiment upon 

 PflUger's Law of Contraction. 



