234 B. MELLAND. 



lines. These bright lines are caused by refraction from the longitudinal 

 rods of the network. 



III. Osmic Acid Preparations. 



Preparations made by placing living muscles from the bee in osmic 

 acid 1 per cent for ten minutes, and mounting in balsam, give on 

 examination the appearances figured in fig. 18 and diag. 6. Thickenings 

 (Engelmann's "fixed waves of contraction") are seen on many of the fibres. 



In diag. 6, l the fibre is seen crossed at intervals by a dark well- 

 marked line, Krause's " membrane," or the horizontal network. On 

 focussing upwards this line appears as a thin bright disc, and the 

 appearance u is obtained. 



In certain fibres (fig. 18), by careful examination, it can be seen 

 that this dark line consists of a row of dots, and occasionally fine 

 longitudinal lines may be seen joining them. 



A fixed wave of contraction is shown in this figure. The contracted 

 part of the fibre is widened out transversely and the distance between 

 the transverse networks diminished. The series of haloes round the 

 rows of dots extends to the whole of the now diminished interval 

 between the successive rows. There is consequently a bright band in 

 the position usually occupied by the dim band. Traversing this bright 

 band longitudinally are seen fine lines joining the dots of adjacent 

 networks. Between this fully contracted and the relaxed part of the 

 fibre is the portion showing the "homogeneous stage " of Engelmann. 

 The transverse marking is here to a large extent lost, and this can be 

 easily understood, when we consider that at the onset of contraction 

 the transverse network would be probably more or less pulled out of 

 shape. The individual dots would no longer lie in the same transverse 

 plane, and hence the haloes would not blend into a continuous bright 

 transverse disc. This agrees with the fact mentioned by Schafer, 1 

 that mechanical shifting of the elements of a fibre causes a dis- 

 appearance of the transverse striations. 



Another point often observed in osmic acid preparations is a caving 

 in of the sarcolemma between each transverse network, that is opposite 

 the dim stripe. In other preparations the sarcolemma usually bulges 

 at these points, and appears to be contracted at its attachment to the 

 transverse network or Krause's membrane. This may be explained 

 if it be supposed that in osmic acid preparations there is a certain 

 1 Quain's Anatomy,' vol. ii, 9th edition, p. 129. 



