50 H. E. JORDAN 
under pressure; normally glass is isotropic, but under pressure it 
develops temporary anisotropic striae. The notoriously feebler 
anisotropy of the contracted fiber may result from a disturbance 
during contraction of the more regularly oriented particles of the 
extended fiber. But the question still remains as to how the 
stratification of the isotropic and anisotropic substances of cer- 
tain fibers is to be explained. In the first place, it should be 
noted that such stratification in otherwise apparently identical 
fibers may be present in one and absent in the other. It may 
be justly claimed that failure to see this stratification is due, in 
a certain number of instances, to unfavorable orientation of the 
fiber under examination. When the stage of the microscope is 
revolved under the crossed nicols, a certain number of these 
apparently inactive fibers give evidence at a certain portion of 
the field of clear stratification. But there still remain a certain 
number of fibers in the relaxed condition, which, when viewed 
under the very best conditions, still are apparently inactive. 
The most favorable condition for detecting the anisotropic striae 
are fixation in alcohol and mounting in glycerine. Regarding 
the apparently optically inactive residue of fibers it might be 
claimed that their inactive condition is due to oblique longi- 
tudinal strains or distortions, disturbing the original segregation. 
Such distortion is almost unavoidable with fresh teased material. 
Previous coagulation of the sarcoplasm with alcoholic fixation 
gives to the anisotropic material a more stable condition and a 
sharper definition. But it is also quite probable that fixation of 
itself brings about a sharper segregation than is characteristic of 
the normal living sarcoplasm. Granting, however, a more or 
less sharp segregation of the anisotropic condition, as we are in 
fact compelled to do for living fibers of insect leg muscle under 
certain normal conditions, the further question remains as to 
why those segregations correspond in general with the limits of 
the dark (Q) dise. ‘The answer to this question follows from the 
fundamental physical condition of the Q-dise. It was shown 
above that the action of alcoholic fixation and the mechanical 
factors of tension both indicated the relatively more fluid 
nature of the substance of the dark disc. Dehydration was 
