it to say that it is a very complex structure, containing apparently contractile matter in the form of discs alternating with discs of a substance that is not contractile but which may
Fig. 48.—Diagram showing hypothetical views as to the structure of striated muscle. Four fibres side by side, a, clear bands or discs, each formed of two clear bands or discs, termed the lateral discs of Engelmann, separated by a thin dark line or band, known as Dobie's line, or Krause's membrane; b, two discs of dark substance, forming the sarcous elements of Bowman, having in the centre an ill-defined band or line, the median disc of Hensen; a is singly and b is doubly refractive as regards light.
possibly be elastic. Further, during life, the whole of this remarkable structure is semi-fluid, and there are good grounds for believing that the contractile action is due to the creation of currents passing from one part of the fibre to another, accompanied by chemical changes of a very complicated kind.
As one would expect, the fibres of muscle are intimately connected with a nerve. But
