THE MUSCULAR SYSTEM 26 1 



center of the elbow joint. From these distances calculate the force 

 with which the biceps contracts in order to support a weight of ten 

 pounds on the palm of the hand. 



13. How does exercise benefit the health ? How does a short 

 walk " clear the brain " and enable one to study to better advantage ? 



14. When exercise is taken for its effects upon the health, what 

 conditions should be observed? 



PRACTICAL WORK 



The reddish muscle found in a piece of beef is a good example of 

 striated muscle. The clear ring surrounding the intestine of a cat 

 (shown by cross section) and the outer portion of the preparation from 

 the cow's stomach, sold at the butcher shop under the name of tripe, 

 are good examples of non-striated muscular tissue. The heart of any 

 animal, of course, shows the heart muscle. 



To show the Structure of Striated Muscle. Boil a tough piece of 

 beef, as a cut from the neck, until the connective tissue has thoroughly 

 softened. Then with some pointed instrument, separate the main piece 

 into its fiber bundles and these in turn into their smallest divisions. 

 The smallest divisions obtainable are the 'muscle cells or fibers. 



To show Striated Fibers. r Place a small muscle from the leg of a 

 frog in a fifty-per-cent solution of alcohol and leave it there for half a day 

 or longer. Then cover with water on a glass slide, and with a couple 

 of fine needles tease out the small muscle threads. Protect with a 

 cover glass and examine with a microscope, first with a low and then 

 with a high power. The striations, sarcolemma, and sometimes the 

 nuclei and nerve plates, may be distinguished in such a preparation. 



To show Non-striated Cells. Place a clean section of the small 

 intestine of a cat in a mixture of one part of nitric acid and four parts 

 of water and leave for four or five hours. Thoroughly wash out the acid 

 with water and separate the muscular layer from the mucous membrane. 

 Cover a small portion of the muscle with water on a glass slide and 

 tease out, with needles, until it is as finely divided as possible. Ex- 

 amine with a microscope, first with a low and then with a high power. 

 The cells appear as very fine, spindle-shaped bodies. 



To illustrate Muscular Stimulus and Contraction. Separate the 

 muscles at the back of the thigh of a frog which has just been killed 

 and draw the large sciatic nerve to the surface. Cut this as high up as 

 possible and, with a sharp knife and a small pair of scissors, dissect it 



