GENEEAL PHYSIOLOGY OF MUSCLE 



29 



Since the experimental conditions adopted by the two authors 

 are essentially different, these apparently contradictory conclusions 

 may not be irreconcilable. 



Both Engelmann and Eanvier agree, though from different 



FIG. 21. (Left.) Fixed wave of contraction in muscular fibre of insect. (Engelmann.) The right 

 half of the figure shows the fibre examined under polarised light ; the doubly refracting bands 

 look light on a dark ground with crossed Nicols. R, segment of fibre at rest ; //, segment 

 beginning to contract ; C, contracted segment, a, intermediate disc of Arnici ; b, accessory 

 disc of clear or isotropous layer ; c, dark or anisotropous layer. 



Fio. 22. (Right.) Fixed wave of lateral contraction near a motor end-plate (Pm) obtained by 

 Rollett from a muscle fibre of Cassida equestris. Very high magnification. 



reasons, in regarding the anisotropous disc as the only contractile 

 part of the muscle fibre. Engelmann based this conclusion on a 

 long series of observations which showed that contractility and 

 double refractivity appear simultaneously during the ontogenetic 

 development of the muscle cells, and that the contractile force is 

 greater in proportion as the double refractivity is more intense. 



