272 THE BODY AT WOKK 



exercises in his bathroom. Failing out-of-door opportunities, 

 much can be done by the systematic use of the various muscles 

 working against resistance. It is alleged, and we are not dis- 

 posed to dispute the justice of the contention, that movements 

 made with the fullest degree of mental concurrence have a more 

 rapid effect upon the growth of muscle than actions more or 

 less unconscious. Muscle and nerve are parts of a single 

 mechanism. It may be that fixing the attention on an exercise, 

 and watching its performance in a looking-glass, aids the 

 nutrition of muscles by increasing the influence of their nerves, 

 possibly by improving the nutrition of their nerve-centre. 

 Unfortunately, this is one of many theories which hardly come 

 within the reach of a control-experiment. Could one concen- 

 trate attention on the movements of the right arm, then absent- 

 mindedly repeat them with equal vigour with the left, it might 

 be possible to ascertain whether there is anything in this idea. 

 Two other contentions with regard to the best way of perform- 

 ing movements, with a view to the promotion of muscular 

 growth, appear to be justified by their results. Working 

 against a moderate or light load is said to be more effective than 

 putting muscles to a severe strain. A small number of 

 maximal contractions, it is said, induce more rapid growth than 

 many partial shortenings. According to this scheme, when a 

 particular muscle needs strengthening, because in a certain 

 action it is to be the chief performer, it is made to bring its two 

 ends as near together as the plan of its attachments allows. 

 Maximal shortening is apparently favourable to blood-supply 

 and otherwise promotes nutrition. 



Tone. Hitherto we have spoken of quiescence and activity, 

 as if muscle were doing nothing when not visibly contracting. 

 A wrong impression may be engendered by these terms. 

 Muscle is never idle. During sleep, and still more when a 

 person is under the influence of anaesthetics, the muscles 

 approach the condition of machines at rest. But again the 

 language of the workshop is inapplicable. When a headless 

 frog is hanging from a hook its legs are slightly bent. All its 

 muscles are weakly contracted, if we understand by contraction 

 a condition in which the length of muscle is less than it would be 

 were it not alive. But the flexors are tenser than the extensors, 

 hence the crooking of hip, knee, and ankle. If the sensory 



