VIII.] STRUCTURE OF CONTRACTILE TISSUES. 83 



gently pull them out to the opposite end. Lay 

 them on a glass slide, and separate them a little 

 in the centre, place a bristle across them and 

 press gently : remove the bristle, put on a cover- 

 slip and let a drop of normal saline solution run 

 underneath it (cp. method, Lesson V. A. 2 a, c). 

 Where the bristle was pressed on a fibre the 

 muscular substance will be seen in many cases 

 to be broken across leaving its delicate trans- 

 parent sheath, the sarcolemma, stretching across 

 the gap ; an indication of the sarcolemma as a 

 fine line bulging out from the muscle substance 

 may also be seen where a fibre is bent. 



5. Irrigate with acetic acid *5 p. c. and observe 



a. The fibres at first become cloudy and semi- 

 opaque. 



b. The precipitate causing this cloudiness is 

 after a while dissolved, and the fibres be- 

 come more transparent than normally. 



c. The nuclei of the fibres come into view scat- 

 tered throughout the muscle substance ; they 

 are elongated in the direction of the fibre : 

 lines of granules proceeding from their ends 

 may usually be seen. 



G. Cut through the skin in the mid ventral line in 

 a small frog, lift up the flap of skin on one side 

 over the middle of the sternum, a thin band of 

 muscle will be seen running from the skin down- 

 wards towards the lower part of the sternum. 



62 



