118 ELECTRO-PHYSIOLOGY CHAP. 



is sooner or later a spontaneous excitation of the nerve-fibres, as 

 shown first in twitches of the fibrils and then in tetanic con- 

 traction of the entire muscle (desiccation- and salt-tetanus). If 

 the excitability of such a nerve is tested from time to time with 

 a current of uniform strength, it is found to increase, until, just 

 before the commencement of desiccatory spasm, each closure, or 

 opening, discharges powerful but irregular tetani. The closure- 

 tetanus of " cooled " nerves, on the contrary, is usually quiet and 

 regular, the curve showing no marked divergence from the 

 tetanus-curve of intermittent excitation. The conjecture that 

 closing and opening tetani are due to abnormal activity in the 

 nerve, is completely contradicted by the fact that the motor 



FIG. 171. Tetanus curve of gastrocnemius on closure of a battery current (closure tetauus). 

 Preparation from a cooled frog. (Von Frey.) 



nerves of other animals invariably react by tetanus, under all cir- 

 cumstances. This applies, according to Eckhardt's observations 

 (5), especially to nerves of warm-blooded animals, when excited 

 with descending currents of average strength, as well as to the 

 non-medullated motor nerves of many invertebrates (claw nerve 

 of crayfish, etc., Biedermaim). In both cases closure-tetanus is 

 the rule and not the exception, and thus du Bois' "universal 

 law " has as little application to indirect as to direct excitation of 

 the muscle. We must rather hold that, although the visible 

 effects of the transmitted excitation are fundamentally due to 

 variations of density in the current flowing through the nerve, 

 the excitatory process is locally initiated throughout its cnfir* 

 jtassage, and that other circumstances determine whether this 

 continuous excitation is expressed at the peripheral organ (muscle) 

 or no. The same applies to the state of activity at break of the 



