XIII J STRIATED MUSCLE 103 



bulgings, the bulgings are opposite the thick disc, the 

 depressions are opposite the thin disc (this may be 

 seen by watching a fibre as it contracts on dying) ; the 

 thick discs are now bright partly in consequence of 

 the moniliform shape of the fibre they are separated 

 from one another by rather broad darker discs which 

 represent the bright band and thin disc of the un- 

 contracted fibre. 



The nuclei, usually round, are imbedded in a 

 granular mass of protoplasm (sarcoplasm) ; the whole 

 forms a band or rod running a variable distance in the 

 substance of the fibre. Irrigate with acetic acid 1 p.c. 

 to make the nuclei more distinct. 



7. Tease out a little of the wing (thoracic) muscle of an 

 insect, note the small cylindrical striated fibres, the sarcostyles, 

 all of nearly the same size, and the large amount of sarcoplasm. 

 The sarcostyles though small are much larger than the fibrils 

 seen in 2. Measure one or two. 



8. Transverse sections of a piece of wing muscle from an 

 insect (Flemming's fluid). Stain on a cover-slip. Note the 

 round areas of the sarcostyles imbedded in the granular proto- 

 plasm. 



9. Examination of muscle with polarized light. Place one 

 NicoFs prism under the stage of the microscope in the position 

 of the condenser. Select a specimen of striated muscle, in which 

 the fibres are isolated, and the planes of the discs at right angles 

 to the stage. Using an ordinary ocular, focus the piece of 

 muscle to be observed. 



Substitute for the ordinary ocular the frame containing an 

 ocular with a Nicol's prism (the analyser) above it. Put the 

 pointer of the analyser at of the scale on the frame. Turn the 

 frame with the analyser round one complete circle. The field 

 during the complete revolution becomes dark twice and light 

 twice. 



