226 THE PHYSIOLOGY OF MUSCULAR WORK 



cannot perceive a note much lower than one of that frequency. 

 It is probable that the muscle note really represents the overtone 

 corresponding to the second octave of the vibration ten a second. 



The work of Horsley and Schafer ( 21 ) shows that the rate of 

 contraction is determined chiefly by the rate of discharge of the 

 nerve cells concerned in the movement. A muscle can contract 

 at a faster rate, a nerve can conduct impulses more quickly than 

 ten a second, if they be stimulated artificially. An interesting 

 contrast is revealed by a comparison of the rates of contraction of 

 a muscle when it is stimulated respectively through the cortex of 

 the brain, the corona radiata, the spinal cord, and the motor nerve. 

 In the last case only is the muscle thrown into such rapid contrac- 

 tion that complete tetanus is produced. 



The rhythm of the muscular response ( 22 ) to volitional impulses 

 in man is about eight to thirteen per second, the number of waves 

 varying in different individuals and in the same individual under 

 different conditions of work. A voluntary contraction is an 

 incomplete tetanus, in which each component is a single con- 

 traction prolonged long enough to produce imperfect fusion of 

 the waves. 



The conditions which affect the activity of the muscles engaged 

 in a simple movement can be studied by the apparatus introduced 

 by Mosso, and called the ergograph. The movements of a ringer 

 or limb are transmitted by a system of levers to a writing point 

 which marks a graphic record of the movement upon a piece of 

 smoked paper fixed to a revolving drum. With this instru- 

 ment many observations ( 23 ) have been made to determine the 

 influence upon the performance of work of practice, the rate of 

 contraction, load, rest, hunger, mental activity, various foods and 

 drugs. Many of the results, however, n^ust be accepted with 

 caution, for there is one source of fallacy whjich has not been suffi- 

 ciently recognised by some investigators ; 'complications can be 

 readily introduced during an experiment by the influence of sug- 

 gestion upon the subjects of the research, and it is not possible to 

 eliminate these entirely by employing as subjects men who have 

 no special knowledge of, or interest in, the research. 



Ergographic studies have shown that general or local fatigue 

 and hunger diminish, while previous practice, r6st, sleep, and food 

 increase the power of voluntary muscular contraction. These 

 results are in accordance with the general experience of mankind, 



