SYSTEMATIC SYNTHESIS OF TISSUES INTO ORGANS. 241 



becomes broader and harder ; when the fore arm is lowered, the muscle 

 returns to its former condition. 



469. Contraction of a muscle could not be continued 

 as long as it now is IF THE ENTIRE MUSCLE CONTRACT- 

 ED at once. 



470. Only A PORTION OF THE CONTENTS OF A FIBRIL 

 contract at a time, when another portion takes it up, 

 then another, then another. Thus there is a vibratory 

 contraction of a muscle during the time that it appears 

 to contract. 



471. ANOTHER PECULIARITY OF MUSCLE is TO BE 

 NOTICED : if it is cut it gapes. The muscle must therefore 

 be constantly contracted to a degree. This is called its 

 tone or its tonicity, and exists without reference to the will. 



472. THE TONE OF THE MUSCLES WILL DIFFER in 

 different persons, and in the same person at different 

 times. Whether it is the same as its contractility, only 

 in a lesser degree, is not known. It can be suspended 

 or diminished by the action of various medicines, for 

 instance, those that sicken the stomach. 



473. It is the tone of the muscles that balances THE 



ACTION OF ONE MUSCLE AGAINST THAT OF ANOTHER, and 



preserves an equilibrium of the parts of the Body. 



474. WHEN MOTION is PRODUCED BY THE CONTRAC- 

 TION OF ONE OR MORE MUSCLES, the relaxation of one or 

 more must take place at the same time. Contraction 

 and relaxation must always be harmonious. 



475. A DOUBLE INFLUENCE MUST ALWAYS BE EXERT- 

 ED in producing motion, one controlling the action of 

 the muscle or muscles directly producing the motion, 

 and another controlling the action of the relaxing or 

 opposing muscles ; and the requirement for the one is as 

 imperious and requires as nice adjustment as the other. 



476. SOME MOTIONS ARE PRODUCED by the direct 

 action of fasciculi, others by the combined action of sev- 



469. What ? 470. What said of ? 471. What is ? 472. How ? 473. What 

 said ? 474. What said ? 475. Why ? 476. How ? 



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