16 LABORATORY DIRECTIONS IN 



different functions. Cells having similar functions combine to form 

 tissues and tissues unite to form organs of various kinds. 



3. Movements. Movements in higher animals are usually due 

 to the concerted action of numerous specialized cells known as muscle 

 cells. 



3a. Examine a longitudinal section of the tail of a young sala- 

 mander. A considerable portion of the section passes through the 

 muscles. Note that the muscle mass is divided into segments, the 

 myotomes, by oblique septa of connective tissue. Muscle cells extend 

 lengthwise from one septum to the next. What is the relative length and 

 width of each cell? (The width can best be determined near the septa.) 

 How many nuclei in one cell? Observe the longitudinal threads or 

 fibrils in the cells. Note the transverse light and dark bands on the 

 fibrils. These are known as striations. Are the striations continuous 

 lines across each cell? 



36. If time permits a bit of teased out preserved frog muscle should 

 be examined for the structures found in the above preparation. An 

 oil immersion demonstration will also be provided showing the structures 

 more in detail. 



Muscular movements are due to changes in the muscle fibrils re- 

 sulting from a change in the relative size and shape of the light and dark 

 bands. The process is not very well understood. Approximately what 

 fraction of the muscle cell is given over to the function of movement? 

 Is the movement performed by the general protoplasm or by specialized 

 structures? 



3c. A muscle removed from the body will respond to various forms 

 of stimuli such as mechanical, thermal, chemical, and electrical. The 

 last is usually employed in laboratory experiments. The contraction 

 of a muscle will be demonstrated by the following experiment. 



The gastrocnemius muscle of a frog is removed and suspended by 

 means of a clamp attached to the leg bone. A small weight is attached 

 to the lower end by means of a hook. The muscle should be kept moist 

 with normal salt solution. Touch the muscle with platinum electrodes 

 attached to a dry cell. Note the contraction. Is the movement slow 

 or rapid? How does the muscle change in shape? How much does it 

 shorten? When does the contraction occur, at the application of the 

 stimulus, during the passage of the current through the muscle, or at the 

 removal of the stimulus? 



3d. In the body the muscle usually responds to stimuli that come to it 

 through a nerve. The conduction of an impulse through a nerve may 

 be demonstrated by a nerve-muscle preparation of the gastrocnemius of 

 the frog. In such a preparation the nerve going to the muscle is left 

 intact. Apply the stimulus to the nerve some distance from the muscle 

 and compare the contractions with those above. 



