STRUCTURE OF STRIATED MUSCLE. 75 



LESSON XVI. 



STRUCTURE OF STRIATED MUSCLE (continued}. 



1. CUT off the head of a beetle or other large insect (e.g. bee, wasp), 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 it is better to mount them either in a drop of white of egg or of 

 the insect's blood. In both preparations the dark-looking air-tubes or 

 tracheae form prominent objects ramifying amongst the fibres. Observe the 

 structure of the two kinds of muscle so far as it can be made out in the fresh 

 preparation. If the preparation is made quickly, waves of contraction will 

 probably be observed passing along the fibres. 



2. Make another preparation, mounting the muscle in vinegar. (Alcohol- 

 hardened muscle may be used for this purpose.) Notice that the muscular 

 substance swells up somewhat and becomes clearer, whilst the sarcoplasm-net- 

 work of the leg muscles, with its lines and dots, comes more distinctly into 

 view. In a well-teased preparation of alcohol-hardened muscle, the leg-fibres 

 will be frequently found breaking across into disks. Make careful drawings 

 from this preparation. 



3. Place an insect (wasp, beetle) into 90 per cent, alcohol for 24 or 48 hours. 

 Then take a small piece of each kind of muscle, and place in strong glycerine 

 for some hours to remove the alcohol. Transfer to 1 per cent, chlo'ride of 

 gold solution : leave the pieces of muscle in this from 15 to 30 minutes 

 according to their size. From the gold solution they are transferred to 

 formic acid (1 part of the strong acid to 3 of water), and kept in the dark for 

 24 hours, but they may be kept longer without disadvantage. The muscle is 

 then teased in glycerine. Some of the fibres will be found after this method 

 to have their sarcoplasm darkly stained, and to show, therefore, the appear- 

 ance of a network both in longitudinal and transverse view : others, on the 

 other hand, have the sarcous elements stained, and the sarcostyles are thereby 

 rendered very evident, but the sarcoplasm is unstained. Some fibres may 

 show an intermediate condition. 



Ordinary or leg-muscles of insects. In the muscles of insects the 

 stripes are relatively broad, and their structure can be more readily 

 seen than in mammals. In the living fibres from the muscles of the 

 legs, the sarcoplasm presents a striking appearance of fine longitudinal 

 lines traversing the muscle, and enlarging within the light stripes into 

 rows of dots. This is still better seen in fibres and portions of fibres 

 which have been treated with dilute acid. In separated disks produced 



