61 



LESSONS XV. AND XVI. 



STRUCTURE OF MUSCLE. 



LESSON XV. 



1. TAKE a shred of muscle from a recently killed mammal, and on a dry slide 

 carefully separate long pieces of muscular fibre (single fibres if possible) and 

 stretch them out, keeping them moist during the process by breathing on the 

 slide. Put a drop of serum on the cover-glass before placing this over the 

 preparation. Study first with a low, then with a high power. Sketch all the 

 appearances to be seen in a small piece of a fibre, focussing carefully the most 

 superficial layers. Notice the oval nuclei immediately under the sarcolemrna. 

 Then allow a little dilute acetic acid to run under the cover-glass and watch 

 its effect. 



2. Prepare some fibres of frog's muscle in the same way, but mount in 

 salt solution instead of serum. Notice the muscular substance shrinking 

 away here and there from the sarcolernrna, which then becomes distinctly 

 visible. Sketch a piece of sarcolemma bridging across an interval thus pro- 

 duced. 



3. Mount in Farrant transverse sections of fresh muscle which have been 

 cut whilst frozen, and at once placed in 1 per cent, nitrate of silver solution. 

 Take care to prevent the cover-glass from pressing on the sections. Examine 

 first with a low and then with a high power. Sketch the appearances which 

 are seen. 



In each of the above preparations measure the diameter of some of the 

 fibres. 



LESSON XVI. 



1. CUT off the head of a water-beetle and bisect the trunk with scissors so as 

 to expose the interior. Notice two kinds of muscular tissue, the one belonging 

 to the legs greyish in colour, the other attached to the wings yellowish. 

 Preparations of both kinds of muscle are to be made in the same way as living 

 mammalian muscle (see previous Lesson), but they are to be mounted either 

 without the addition of any fluid or in a drop of the insect's blood. In both 

 preparations the dark-looking air-tubes or trachea form prominent objects 

 ramifying amongst the fibres. Observe the structure of the two kinds of 

 muscle, noting especially the fine fibrils of the wing muscles and the muscle- 

 rods in the large fibres of the leg muscles. If the preparation is made quickly, 

 waves of contraction will probably be observed passing along the last-named 

 fibres. 



The remainder of the water-beetle may be put into spirit (pinned upon a 

 cork so that the muscles are well stretched) and preparations made on a 

 future day after the manner described in the next preparation. 



2. Place in logwood a small shred of mammalian muscular tissue which 

 has been stretched upon a cork and hardened in alcohol. When it is deeply 



