THE MUSCULAR MOTOR AND ALIMENTATION 119 



by means of special apparatus (the myophone). Hence the 

 motor excitantation is periodic, and owing to muscular elasticity, 

 there is in the process a " latent addition " due to the nervous 

 shocks. 



Shin 



Muscle 



FK. 123 

 Reflex sensi -motor arc. 



I, In spite of this fusion of impulses voluntary contraction is more 

 rapid than the contraction due to electric shock, for it can last 

 T $^ of a second, with a maximum of 16 contractions per second 

 each corresponding to three impulses (see 90) . 



It the excitation is external, as in the case of a person abruptly 

 brought face to face with a danger, or touching, inadvertently, 

 a burning substance, a reflex phenomenon is produced, since the 

 elements of the sensitive neuron S, awakened by the burning of 

 the skin (fig. 123) transmit the sensation to the motor neuron M, 

 which acts on the muscle and contracts it. 



.Movement will therefore follow the sensation. 



Excitation travels along the nerves at an average speed of 32 

 metres per second^ 1 ) but the total duration of the reflex action 

 is prolonged because very often several neurons are intercalated 

 in the path. 



(*) F. Kiesow (Arch. Ital. Biol., vol. xl., p. 273, 1903). Piper gives 

 120 metres as the result of his researches on the brachial nerve. 



