TONE-INDUCTORIUM OF KRONECKER AND STIRLING. 



487 



Duration of Tetanus. A tetanised muscle cannot remain contracted to the same extent for 

 an indefinite period, even if the stimuli are kept constant. It gradually begins to elongate, 

 at first somewhat rapidly, and then more slowly, owing to the occurrence of fatigue. If the 



Fig. 335. 

 Make and break induction shocks of 300 units, applied at intervals of a second to the pale 

 (lower) and red (upper) muscles of a rabbit. The lowest line marks second {Kronecker 

 and Stirling). 



tetanic stimulation is arrested, the muscle does not regain its original position and shape at 

 once, but a contraction -remainder exists for a certain time, this being more evident after stimu- 

 lation with induction shocks. 



IV. If very rapid induction shocks (224 to 360 per second) be applied to a 

 muscle, the tetanus after a so-called " initial contraction " (Bernstein) may cease 

 (Heirless, Heidenhain). This occurs most readily when the nerves are cooled. 

 Kronecker and Stirling, however, found that stimuli following each other at greater 

 rapidity than 24,000 per second produced tetanus. 



[Tone-inductorium of Kronecker and Stirling. This apparatus (fig. 336), consists of a rod 

 of iron, d, fixed in an iron upright at a. The primary, s and secondary spiral, s n , rest on 

 wooden supports, which can be pushed over both ends of the rod. One end of the rod lies 



Fig. 336. 



Tone-inductorium of Kronecker and Stirling, d, iron rod, clamped at a ; s primary, s lt , 



secondary spiral, with a key, k ; leather rollers, / and g, driven by wheels, h. 



between leather rollers, /and g, which can be made to rub on the rod by moving the toothed 

 wheels, h. In this way a tone is produced by the longitudinal vibrations of the rod, the 

 number of vibrations being proportional to the length of the rod, so that by means of this 

 instrument we can produce from 1000 to 24,000 alternating induction shocks per second.] 



Fick has recently investigated the changes tension undergone by a muscle when it is 

 stimulated, and when its length remains constant, and he calls this process an ' ' isometrical 

 muscular act." He finds that a voluntary contraction in an isometrical act in man causes a 

 higher tension than a contraction excited electrically. In the frog, the tension is nearly twice 

 as great during tetanus as during a single jliaximal muscular contraction ; in human muscles, 

 it may be ten times as great. 



299. RAPIDITY OF TRANSMISSION OF A CONTRACTION. 1. If along 

 muscle be stimulated at one end, a contraction occurs at that point, and is rapidly 



