338 Dr. K. Sassa. Observations on Rejiex 



a like stimulus (5, 16). If excitation is applied longer at this rate the 

 direct tetanus increases in power, while the reflex tetanus decreases, or 

 slowly increases, only to decrease later, so that the former always surpasses 

 the latter in 'the maximal power produced. This indicates that fatigue is 

 more easily ; produced in the central than in the peripheral mechanism. 



At the optimal rate of stimulation the reflex contraction is often nearly 

 as powerful and abrupt in the first period of tetanus as the direct one 

 (fig. 4). If the excitation is prolonged, the direct tetanus soon attains the 

 maximum, which is maintained for a long time, while the reflex tetanus 

 diminishes in height. The difference of the maximal contraction in both 

 cases is often extremely slight in good preparations. This observation 

 suggests that the spinal centre is a physiological unity, any one afferent nerve 

 being connected with all the motor neurons of the reflex arc, since there is 

 some evidence that each component shock of faradisation applied to an 

 afferent nerve at the rate of more than 50 per sec. is followed by only one 

 motor impulse, not by a group of impulses (1). The result more usually 

 obtained, that reflex tetanus falls more or less short of direct tetanus, is 

 partly due to the fact that the reflex centre is more easily fatigued than the 

 muscle itself. It must further be remembered that it is often difficult to 

 make out exactly the optimal intensity. At rapid frequency of stimulation 

 the direct is usually more powerful than the reflex tetanus. 



Fig. 4. — Semitendinosus preparation. Comparison of reflex (P) with maximal direct 

 tetanus (M). D = frequency 45 per sec. and 20 cm. ; E = 60 per sec. and 18 cm. ; 

 P = peroneal nerve stimulation. M = sciatic roots stimulation. Time in sec. 



The afferent nerves hitherto used were nerve trunks, siich as the tibialis, 

 peroneus, or sciatic. The extent of the reflex contraction produced by stim- 

 ulating these afferent nerve trunks slwws only small differences. A stronger 



