70 PHYSIOLOGY OF MUSCLE AND NERVE 



CHAPTER VI 

 THE CHARACTER OF THE CONTRACTION OF MUSCLE 



The Simple Twitch. — In accordance with the frequency and char- 

 acter of the stimulus, striated muscle reacts by giving either a simple 

 twitch-like contraction or a prolonged contraction, known as tetanus. 

 The former is obtained whenever the muscle or its motor nerve is 

 excited with a single stimulus, whether it be mechanical, electrical, 

 thermal or chemical. A graphic record of it may be made by con- 

 necting the muscle with a writing lever in the manner described 

 previously. If the kymograph is permitted to remain stationary, the 

 contracting muscle registers merely a straight line approaching the 



Fig. 37. — A Muscle Twitch. 

 M, make shock recorded by magnetic signal connected with primary circuit. Time 

 ill Hoo sec. ; L, latent period ; C, period of contraction ; R, period of relaxation. 



vertical, whereas a revolving kymograph will tend to separate the up 

 and down strokes more and more as its speed is increased. The result 

 is a wave-hke curve, possessing a certain height and length. A tuning 

 fork, carrying a marker upon one of its prongs, is usually permitted to 

 register its vibrations below the writing lever of the muscle. More- 

 over, if the electrical method of stimulation is employed, the moment 

 at which the shock is thrown into the muscle or its nerve, may be 

 registered by means of an electro-magnetic signal which is inserted in 

 the primary circuit and is permitted to write in the same ordinate as 

 the other levers. 



If a muscle-curve of this kind is studied in detail, it is seen to con- 

 sist of two principal phases, namely a period of contraction and a period 

 of relaxation. During the former the muscle shortens until it has 

 attained its state of maximal contraction, while during the latter it 

 relaxes until it has again reached its natural length and form. If a 

 comparison is now made between this curve and the record of the signal 



