Physiology. — ''Tonus and farad ic teianus'. Hy Prof. J. K. A. Wkkt- 

 HKiM Salomonson Eiid Mi's. Ratu Langi — Houtman. 



(Communicated in the meeting of April 26, 1918). 



If a muscle be stiiilulated witli flie secondary current of an 

 indnction apparatus fitted with a vibrating interrupter we generally 

 get a tetanic contraction. In case of a snfficienlly iiigli rate of inter- 

 ruptions per second the tetanus will be a complete one, during 

 which no rapid variations of length, thickness or tension of the 

 muscle can be detected. If the i-ate of stimulation be lessened, the 

 tetanus ceases to be a complete one. Synchronous with the stimuli 

 the muscle shows a series of small twitches superposed on a tetanic 

 contiaction. These can easily be recorded on a rotating drum eitlier 

 by recording the length, the thickness or the tension of the muscle. 

 The twitches become slighter by increasing the rate of stimulation. 

 With a certain I'ate, which we shall call the critical frecpiency, they 

 disappear altogether and we get again a smooth curve, indicating 

 a complete tetanus. 



This critical frequency, with human muscles at least, is fairly 

 constant and varies only very slightly in different muscles from a 

 mean of about 18 per second. But is this critical frequency really 

 a constant one? Do we know of any condition, which might likely 

 cause a variation ? 



A complete tetanus is obtained when the frequency of the exci- 

 tations is such that the intervals l)etween them are equal to the 

 time required for the muscle, excited by a single instantaneous 

 stimulus under isometric conditions, to obtain its greatest tension 

 (BuRUON Sanderson). Marky and Hermann among others state that 

 the time between two stimuli should be a little less than the time 

 t^ken by the muscle to reach its greatest tension after excitation 

 by a single induction-shock. Only changes in the lime covered by 

 the shortening period of the muscle may be able to cause a change 

 in the critical frequency. It is generally known that leniperature 

 changes and exhaustion alter the form of contiaction and that both 

 act on the ascending part of the curve. With human muscles the 

 .influence of temperature, if any, need jiot be considered, and in our 



61 



Proceedings Royal Acad. Amsterdam. Vol. XXI. 



