124 ELECTRO-PHYSIOLOGY CHAP. 



equal to, or smaller than, the duration of twitch up to the 

 moment of maximal shortening. It follows immediately from 

 this, that to yield a complete tetanus the single stimuli must 

 succeed each other the more rapidly in proportion with the 

 shortness of the twitches. In the case of a twitch as rapid as 

 that of the wing-muscles of certain insects, which lasts hardly 

 -J^-Q sec., more than 300 stimuli per sec. would be required to 

 produce a tetanus. When in other cases the contraction, as in 

 the muscles of the tortoise, lasts about 1 sec., two stimuli 

 per sec. will produce complete tetanus. This is most striking 

 in the smooth muscles, which are so sluggish that it is conceivable 

 that an incomplete tetanus may be produced, even when the 

 single stimuli (repeated closure of a constant current of adequate 

 strength) are separated by pauses of several seconds. 



The following numbers give an approximate idea of the 

 stimulation frequency per sec. required to produce tetanic fusion 

 of twitches : 



Tortoise .... 2 (Marey) 



Frog, Hyoglossus (slow) . . 10 to 15 



Gastrocnem. (quick) . . 30 



Crab, Claw-muscle (slow) . . 20 (Richet) 



Tail-muscle (quick) . . 40 



New-born animal (warm-blooded) . 16 (Soltmann) 



Rabbit (red muscle) . . 4 to 10 (Kronecker and 



Stirling) 



(pale) . . . 20 to 30 



Bird . . . .100 (Richet) 



Insects . . . . 300 to 400 (Marey, Landois) 



It is obvious that the above figures would vary considerably 

 if the state of the muscles were to alter. We have already 

 emphasised the difference in duration of twitch according as the 

 muscle at the time of experiment is fresh or fatigued, with 

 circulating blood or bloodless, is normal or poisoned (veratrin), 

 warmed or cooled, so that without changing the frequency of 

 stimulation we may have, according to the physiological state of 

 the muscle, complete or incomplete tetanus, or only simple 

 twitches. Moreover, a glance at the table given above shows what 

 a significant difference exists in the stimulation - frequency 

 required to tetanise functionally different striated muscles in the 

 same animal. As these relations are of great importance, they 

 must be examined more in detail. Eanvier (13) first drew 



