THE MUSCLES 39 



muscle, while gaining in thickness, loses in length in the same 

 proportion; and thus the volume remains the same in action 

 and at rest. 



11. Contraction is not the permanent, or normal state of a 

 muscle. It cannot long remain contracted, but after a time it 

 wearies, and is obliged to relax. After a short rest it can then 

 again contract.' It is for this reason that the heart can beat 

 all through life, night and day, by having, as we shall here- 

 after see, a brief interval of rest between successive contrac- 

 tions. For the same reason, it is more fatiguing to stand for 

 any great length of time in one position, than to be walking 

 for the same period. Intimately associated with muscular 

 tissue in all parts of the body is more or less fat, or adipose 

 tissue. It is especially abundant directly under the skin, to 

 which it gives an appearance of plumpness and smoothness. 

 In prolonged illness, where emaciation is the result, the body 

 uses the stored-up fat for nourishment. Fat also gives symme- 

 try to the body, serves as cushions, and protects from sudden 

 changes of temperature. The histology of adipose tissue shows 

 that the fat cells are very simple in construction. They are 

 usually round or oval in shape, possessing a cell wall, enclos- 

 ing a globule of fat. The nucleus of the cell from which it 



rapidity, following every imaginable combination, and yet the hand gliding 

 over the instrument incessantly changes its position. Sometimes a single 

 finger produces an isolated note ; sometimes two or three act simultane- 

 ously to produce a concord ; while a fourth, striking a string with increas- 

 ing rapidity, produces a trill which rivals the nightingale. Add to all 

 these the modifications necessary to swell the sound or let it die away 

 all, in a word, that constitutes musical expression and it will be admitted 

 that this mechanism is allied to the wonderful, and that it surpasses the 

 most perfect productions of human art." A further idea of the rapidity 

 of the hand's movements is given in the playing of a skilful pianist, whose 

 hands, oftenest occupied together, produce on an average six to eight 

 notes at a time, or about 640 notes in a minute in medium time, and 960 

 notes in extremely quick time. The Wonders of the Human Body. 



11. Is contraction the normal state of the muscle ? Can this state be permanently 

 maintained ? How is the beating of the heart maintained ? Why is it more fatiguing to 

 stand for any great length of time in one position, than to be walking for the same period ? 

 What is adipose tissue f What purposes does it serve ? Describe the structure of fat 



