64 Life and Health 



ADDITIONAL EXPERIMENTS 



Experiment 25. To examine the minute structure of voluntary 

 muscular fiber. Tease, with two needles set in small handles, a bit 

 of raw, lean meat, on a slip of glass, in a little water. Continue 

 until the pieces are almost invisible to the naked eye. 



Experiment 26. Place a clean, dry cover-glass, of about the width 

 of the slip, over the water containing the torn fragments. Absorb 

 the excess of moisture at the edge of the cover by pressing a bit 

 of blotting paper against it for a moment. Place it on the stage 

 of a microscope and examine with highest obtainable power, by 

 light reflected upward from the mirror beneath the stage. Note the 

 apparent size of the finest fibers ; the striation of the fibers, or mark- 

 ings of alternate dim and bright cross bands. 



/Experiment 27. To show the ligamentous action of the muscles. 

 Standing with the back fixed against a wall to steady the pelvis, the 

 knee can be flexed so as almost to touch the abdomen. Take the 

 same position and keep the knee rigid. When the heel has been but 

 slightly raised a sharp pain in the back of the thigh follows any 

 effort to carry it higher. Flexion of the leg to a right angle increases 

 the distance from the lines of insertion on the pelvic bones to the 

 tuberosities of the tibia by two or three inches an amount of 

 stretching these muscles cannot undergo. Hence the knee must be 

 flexed in flexion of the hip. 



Experiment 28. A similar experiment may be tried at the wrist. 

 Flex the wrist with the fingers extended, and again with the fingers 

 in the fist. The first movement can be carried to 90 per cent, the 

 second only to 30 per cent, or in some persons up to 60 per cent. 

 Making a fist had already stretched the extensor muscles of the arm, 

 and they can be stretched but little farther. Hence, needless pain 

 will be avoided by working a stiff wrist with the parts loose, or the 

 fingers extended, and not with a clenched fist. 



NOTE. A description of an apparatus, illustrating the combined 

 action of muscles and joints, may be found in the Outlines of Require- 

 ments for Harvard University. 



