OPTICAL rROPERTIES OF MUSCLE. 113 



either side, jnst as a minute oil-globule in water appears surrounded 

 with a bright halo when examined under the microscope. According 

 to this view the proper substance of the muscle may be re"- 

 garded as consisting of a homogeneous ground-substance, in which 

 lie imbedded successive series of rod-shaped particles, the enlarged 

 ends of which give the appearance of transverse lines of dots, and, 

 by diffraction, produce a relatively bright appearance in their im- 

 mediate neighbourhood, and therefore rise to the bright bauds.* In 

 transverse section the muscle rods appear, if the mus'cle be perfectly 

 fresh, as minute round dots in the homogeneous ground-substance (fig. G9). 



Fig. 69. Fig. 70. 



Fig. 69.— Transverse Section of a Small Muscular Fibre op "Water-Beetle. 



Highly Magnified. 



s, sarcolemma. 

 Fig. 70. — Transverse Section of Portion of Muscular Fibre of Lobster. ExA3iixin> 



IN Salt Solution (}, percent.) and Magnified 400 Diameters (Kolliker). 

 The polygonal areas of Colinlieim are seen, and among tlicm two or three irregular nuclei. 



Under certain circumstances, especially on tlic addition of any fluid, 

 this appearance vanishes, and the ground becomes parted off into 

 definite polygonal areas (Cohnheim's areas) bounded by clear bright 

 lines (fig. 70). These are regarded by Kolliker as the sections of the 

 muscle-columns described by him ; by W. Krause as the ends of minute 

 prisms of which he conceives the muscular substance to be made up. 

 They are not observable in the unaltered condition of the fibre. 



There is every reason to believe that the ground-substance is similar 

 in nature to ordinary protoplasm but without the granular character 

 commonly, but not always, exhibited by the latter. Like the substance 

 composing the plain mus'cular cells shortly to be described, it is doubly 

 refracting (anisotropous), whereas the substance composing the muscle- 

 rods is probably singly refi'acting (isotropous). 



* This view of the cause of the appearance is supported bj' the fact that in certain fibres the 

 ends of the rods are not enlarged, and in such cases the bright transverse stripes are no 

 longer observed. It also explains, amongst other things, why it is that, until quite lately, 

 observers have failed in recognising the actual continuation of the rod-shaped particles 

 into the dots. For a more extended account of the subject, as well as a notice of 

 the recent literature, the reader is referred to a paper on " The Alinute Structure of the 

 Leg-muscles of the Water-beetle " in the Philosophical Transactions for 1873. 



VOL. II. I 



