CRAB'S MUSCLE. 49 



Action of acetic acid. Irrigate with a drop of the reagent, 

 the fibre becomes transparent and the nuclei are seen distinctly 

 inside it. 



Crab's muscle, fully extended, (p.) Rutherford's method. Crab's 

 legs are fastened to pieces of wood in the positions of flexion and of 

 extension. The flat sides of the carapaces of the proximal segments 

 are removed. Treat as follows : 1. Fix 24 hours in formol (1 to 9 water). 

 2. 24 hours to some days in methylated spirit. Tease a piece of the 

 muscle finely in a longitudinal direction, treat it for two minutes with 

 glacial ascetic acid, wash with water, stain in strong aqueous eosin two 

 minutes, wash and mount in glycerin. 



The broad dim stripe is stained of a deep red, 1 and consists 

 of a number of rodlike bodies (sarcous elements) with a slight 

 central swelling (position of Hensen's stripe). The light stripe 

 exhibits the narrow dim stripe or Dobie's line (Krause's mem- 

 brane) running across it ; to each side of this find egg-shaped 

 granules, Fidget's elements (Englemann's accessory disc). The 

 distinctness of the latter will depend upon the degree to which 

 the muscle has been stretched. 



Crab's muscle contracted, (p.) In the same manner as the 



vr / 



above. This shows only a system of dim stripes closer together 

 than and intervening light stripes without any appearance of 

 the narrow Dobie's line. The clear stripe of the uncontracted 

 state has in reality disappeared and the present dim stripe 

 occupies its position. What now appears as the light stripe 

 occupies the place of Henson's stripe. The stripes are thus 

 reversed. 



To see the broadening of contracting fibres the living structure 

 must be examined' 2 , such as the leg muscle of dytiscus marginalia 

 or hydrophilus pisceus, in salt solution or white of egg. 



'Rutherford used the term "chromatin" to designate the stained portion. 

 2 See tongue of frog, pg. 63. 



