16 



ELECTRO-PHYSIOLOGY 



CHAP. 



a 



We further learn with regard to the finer structure of these 

 muscle-cells, from transverse sections, that the proportion between 

 cortical and medullary substance varies enormously in different 

 elements of the same section. " The cortex may be small, and 

 enclose a larger axial hollow, while other adjacent sections show 

 a broad ring, with a narrow central lumen " (different states of 

 contraction). In nearly all muscle-cells, especially in stained 

 preparations of the cross-sections, it is possible to detect a radial 

 striation of the cortical substance, similar in all respects to that 



described above in the 

 muscle -cells of Nematoda 

 and Annulata, and therefore 

 to be interpreted as the ex- 

 pression of a fibrillated 

 structure (Fig. 9). 



There is a regular alter- 

 nation of dark and light 

 striation, and it is easy to see 

 that the dark lines correspond 

 with cross -sections of the 

 spiral fibres, which must ac- 

 cordingly be flat and band- 

 like, while the colourless 

 radii represent an intermedi- 

 ate substance. This appears, 

 inter alia, from the fact that 

 in focussing a thicker cross- 

 section of a muscle-fibre " the 

 dark lines all run out simul- 

 taneously in the same direction like the spokes of a wheel," when 

 the tube of the microscope is gradually lowered. The spiral fibres 

 of the cortex therefore form flat bands, which run in a single layer 

 throughout its entire thickness. These spiral lamellae obviously 

 correspond with the radial " fibrillar laminae " of the muscles 

 described above, and exhibit a further differentiation into delicate 

 homogeneous fibrils, the proper elements of the cortex. The 

 reaction of these muscle-fibres to gold chloride is of great interest, 

 especially in view of certain facts which we shall discuss later. 

 Only the axial sarcoplasm is stained under some conditions, together 

 with the interstitial substance that separates the spirals of the 





FIG. 8. Segment of isolated muscle-cell from Sepiola 

 Rondeletii under (a) high, (V) medium, and (c) low 

 power. (Ballowitz.) 



