STRIPED MUSCLE OF WASP 55 
substance’ within the sarcostyles. Finally, all of the definite 
morphologic data are in direct contradiction of the ‘facts’ upon 
which the imbibition hypothesis is based. In simplest terms, 
as adopted by McDougall and supported by Meigs, the hypoth- 
esis regards contraction and relaxation as phenomena directly 
comparable to the results of the action of hypotonic and hyper- 
tonic solutions, respectively. On the contrary, the evidence 
strongly indicates that contraction depends upon (or is at least 
associated with) essentially intrasarcostylic movements of the 
dark substances (consisting in part at least of chlorides, phos- 
phates and potassium salts) from the middle to the ends of the 
sarcomeres, that is, from the mesophragma to the telophragmata. 
This movement is probably associated with surface-tension, or 
electrocapillary, reactions among the ultramicroscopic particles . 
of the intrafibrillar sarcoplasm. 
Most previous investigators have assumed that the substance 
of the light disc is relatively more fluid than that of the dark 
disc, and that the intrasarcostylic movement of fluids in con- 
traction is from the light disc toward the dark disc, that is from 
Zto M. This is the view of Englemann and of Schaefer. But 
it was shown above that the results of the action of mechanical 
and osmotic factors demonstrate the relatively more fluid nature 
(fundamentally, that is, aside from the presence of granules in 
suspension) of the dark disc. And the histologic preparations 
actually demonstrate, as shown by the staining results, that a 
deeply staining substance passes from Q to J, from M to Z. 
Moreover, if a ‘hyaline substance’ passed in the opposite direc- 
tion, as assumed by Schaefer, thus diluting the dark substance 
of the sarcous elements and so causing it to stain less deeply 
(thus giving the illusion of a reversal of striation), the loss of 
the deeply staining property should appear first along the 
terminal borders of the Q-disc rather than along the midline, as 
is actually the case. 
f. Intercalated discs 
The foregoing bears directly upon the question of the signifi- 
cance of the intercalated discs. In a number of earlier papers®: *!! 
