202 



PHYSIOLOGY 



rests nearly entirely on experiments with frog's muscle, really has reference to 

 a mixed muscle, i.e. muscle containing both red and white fibres. 



Since the sarcous element represents the contractile unit of the 

 muscle, a knowledge of its intimate structure should be of great 

 importance for the theory of muscular contraction. Unfortunately, 

 however, we are here at the limits of the jdemonstrably visible. It 



r ^** 



FIG. 38. Fibrils of the wing-muscles of a wasp, prepared by Reliefs method. 



Highly magnified. (E. A. SCHAFER.) 



A, a contracted fibril. B, a stretched fibril, with its sarcous elements 

 separated at the line of Hensen. c, an uncontracted fibril, showing the 

 porous structure of the sarcous elements. 



becomes difficult to determine how far the appearances observed 

 under the microscope are due to actual structural differences or are 

 produced by the unequal diffraction of light by the varying elements 

 of the muscle fibre. All observers are agreed that the essential 

 contractile element is the row of sarcous elements forming the muscle 

 fibril or sarcostyle. Schafer, working on the highly differentiated 

 wing-muscle of the wasp, concludes that each sarcostyle is divided by 

 Krause's membranes (the lines in the middle of each light stripe) into 

 sarcomeres. Each sarcomere contains a darker substance near the 

 centre divided into two parts by Hensen's disc. At each end of the 

 sarcomere the contents are clear and hyaline. In the act of contraction, 

 the clear material flows, according to Schafer, into tubular pores in 

 the central dark material. 



