10 H. E. JORDAN 
staining portions along the right border of the figure (N, Z, 
and the separated halves of Q) as anisotropic in physical consti- 
tution. Accordingly, he interprets the contraction band as 
composed of the anisotropic substance which was segregated 
within the Q dise in the relaxed fiber. The question of the 
distribution of the anisotropic substance at different functional 
phases will be fully discussed below. It will suffice here to 
point out that Rollet identifies the anisotropic with the deeply 
staining substances of the sarcoplasm. It may be stated now, 
in anticipation of the subsequent fuller discussion, that the 
anisotropic constituent of the sarcoplasm maintains no precise 
correspondence with the deeply staining portions of the 
sarcostyle. 
Two other points pertaining to this illustration must be 
touched: the festooning of the sarcolemma and the absence of 
sarcomeres in which the Q dise is undivided. A festooned 
sarcolemma is not an invariable coincidence of contraction. It 
may be claimed that in general the festooned condition of the 
sarcolemma is a fixation artifact. As to the second point, the 
right-hand border of the fiber here illustrated is probably not 
in extension (nor in relaxation), as is assumed by Rollet. At 
A I have added a diagram of two sarcomeres to illustrate the 
condition of a fiber in repose. The dark dise is not divided 
by the presence of an H disc. Rollet’s fiber is at a midphase 
of contraction at the right. The occurrence of an H disc is a 
coincidence, and an index, of contraction. The type of fiber 
shown at A is a very common one in microscopic preparations. 
If the fiber of Rollet’s figure were actually extended at the 
right, then somewhere between the right and left (contracted) 
borders of the illustration we should expect to find a condition 
like that shown at A. As will be made clear below, the illus- 
tration, A, represents a sarcomere in repose. Such a fiber, 
in the extended condition, would simply have a longer (thicker) 
Q disc. I interpret Rollet’s figure as illustrating a fiber at 
midphase of contraction at the right, in full contraction at the 
left. 
In my study with Banks of intercalated dises in heart muscle,“ 
I based my interpretation of the significance of these discs on 
