MUSCULAR ACTIVITY 49 



tain them. Thus, in spite of thousands of years of dis- 

 use, we still retain the muscles which presumably at 

 some time moved the ears of our ancestors. 



Influence upon other organs. As we have seen, the 

 muscular energy of animals and man is derived from 

 the combustion of the food materials furnished by plants 

 and animals. A sufficient diet is therefore essential, if 

 our muscles are to do their work easily and well. Since 

 the muscles constitute a large part of the active tissues 

 of the body, a correspondingly large proportion of the 

 food which we eat finds its way to them. The digestive 

 system prepares this food for their use. The blood 

 conveys it to them and takes away the waste products 

 of their activity. The lungs and kidneys remove these 

 waste products from the blood. And, finally, their ac- 

 tivity as a whole is controlled by the nervous system. 

 We can thus see that the muscles are responsible for 

 a large part of the body's activity. As a result, the 

 amount of work which the muscles are called upon to 

 do determines very largely not only the growth and de- 

 velopment of the muscles themselves, but the activity 

 and development of the other organs of the body as 

 well. 



EXPERIMENTS AND DEMONSTRATIONS 



Materials : Frog killed by ether or chloroform ; a slice of meat 

 cut across the grain, such as a low cut of the leg including the 

 bone; normal salt solution (l l / 2 drs. table salt to 1 qt. water). 



1) Dissect away the skin of frog's leg and note the outlines 

 of muscles ; the tendon attachments ; and the relation of muscles 

 to joints. Sketch observations. 



2) Examine in a slice of meat the cross sections of muscle 

 bundles. Also note and sketch the connective tissue in its rela- 

 tion to the muscle bundles; the surface tendons; and the inter- 

 muscular tendons. 



