AND PHYSIOLOGY. 



109 



possessor a very delicate sense of the amount of their contrac- 

 tions. 



It is also an established fact that a peculiar rumbling sound 

 is given off and heat evolved during muscular contraction, 

 the latter of which is easily explained by the increased mus- 

 cular waste, or the absorption of oxygen and evolution of car- 

 bonic acid. 



272. Precision of Muscular Contraction— An astonish- 

 ing precision in contraction of muscles is seen in those of the 

 human larynx. The largest of these muscles is less than 

 three fourths of an inch, and the total amount of contraction 

 one fifth. And since the ordinary compass of the human 

 voice is two octaves, or twenty-four semi-tones, and ten inter- 

 vals between each of the contiguous semi-tones can be easily 

 detected by a person with a cultivated ear, there must be a 

 shortening of only joV oth of an inch. And more wonderful 

 than all is the precision and readiness with which an ordinary 

 singer can accurately strike one note after another with inter- 

 vals of from two to twenty-four semi-tones. 



HYGIENIC INFERENCES. 



273. — 1 Muscles need Use —The muscles should be used. 

 This is necessary to stimulate the blood-vessels and lymphatics 

 to a healthy action, so that the nutritious particles may be 

 deposited in proper proportion, and the waste particles be re- 

 moved ; in other words, to promote that constant change 

 which in all the organs of the body is so necessary for health. 

 Their moderate use also promotes their growth and strength, 

 while inaction causes them to diminish both in strength and 

 size. 



Speak of sound and heat attendant upon muscular contraction. 272. What remarkable 

 precision is there in many muscular movements? 273. Why is it necessary that the 

 muscles be used to a moderate extent ? 



