HISTQLOGICAL DEMONSTRATIONS. 93 



oblong particles, which have been conveniently named sar- 

 cons prisms. A fibril consists of these prisms united end to 

 end ; a disc is formed by their transverse union. 



If striped muscle be partially digested in such a digestive 

 fluid as that mentioned in 223 b, it, as has long been 

 known, becomes very apt to split into discs. 



142. Examine, with a power of 800 or 1000 diam., 

 a preparation of the muscle of a bee, hardened in % per 

 cent chromic acid, and mounted in glycerine. The sarcous 

 prisms are beautifully seen. The house-fly and the water- 

 beetle serve equally well for making such specimens. 



143. Amputate the leg of a water-beetle (Dytiscus mar- 

 ginalis}. With a knife slit open the chitinous case ; care- 

 fully pick out the muscle ; make a vertical section with 

 scissors ; add a drop of salt solution, or, still better, aqueous 

 humour ; gently separate the fibres with needles ; cover, and 

 examine without delay. (H.) Observe the contraction 

 waves sometimes implicating the whole thickness, sometimes 

 only a part of the fibre. The stripes are easily seen. Faint 

 dark lines are seen crossing the dim stripe at right angles 

 to it. These are the lines through which longitudinal 

 cleavage of the fibre takes place. 



When magnified 1000 diam. or so, the fine longitudinal lines 

 crossing the broad dim stripe at right angles may be traced into the 

 clear stripe on each side, near the middle of which each line becomes 

 enlarged and forms a knob-like extremity. The whole has been com- 

 pared by Mr. Schaefer to a dumbbell with a very slender shaft. He 

 has termed these structures "muscle rods." The heads of the rods 

 form the faint dark line in the dim stripe. The discussion regarding 

 the cause of the stripes of muscle cannot be entered into here ; but it 

 may be safely said that the whole question is still very obscure. 



144. Examine (H.) striped muscle stained with carmine. 

 The nuclei are stained, but not the sarcous substance or 

 the sarcolemma. 



145. Examine (H.) a T. S. of striped muscle, hardened 

 in chromic acid. Such a section as this will be obtained 

 in a T. S. of the tongue ( 185). The fibres are seen to be 

 polygonal, owing to collateral pressure. In the living 

 muscle they are rounded. 



