CHAPTER VI. 



THE BEHAVIOUR OF MUSCULAR FIBRES WHEN EXAMINED 

 BY POLARISED LIGHT. 



BY E. BRUCKE. 



WHEN muscular fibres are examined with a microscope to 

 which a polarising apparatus is attached, remarkable and 

 instructive phenomena are observed. If the field be darkened 

 by crossing the planes of polarisation of the Nicol's prisms, those 

 fibres only disappear which lie parallel to the plane of polari- 

 sation of one or other of the prisms ; the rest, which cut those 

 planes at various angles between and 90, appear of a grey 

 colour upon a black ground, the most distinct being those which 

 cut them at an angle of 45. In those parts where the muscu- 

 lar fibres running parallel with one another are arranged in 

 several layers, the colour assumes a whitish tint, passing 

 into yellow. The tint varies with the thickness of the layers, 

 precisely as the succession of colours in Newton's rings, from 

 the centre towards the circumference. If one of the Nicol's 

 prisms be turned to the extent of 90, so that the field becomes 

 clear, and attains its maximum brightness, the complementary 

 tints make their appearance. These phenomena, with others 

 that will presently be described, are equally apparent when the 

 muscular fibres are thoroughly impregnated with, and sur- 

 rounded by, strongly refracting fluids, as glycerine, turpentine, 

 and Canada balsam. This is essentially owing to the circum- 

 stance that the muscle substance is doubly refractile, two 

 systems of undulations propagating themselves according to 

 different laws, and interfering the one with the other. 



This explanation had already been given in 1839 by 



T 



