STRIPED MUSCLE OF WASP 23 
pretation, sarcostyle C is in a condition of repose, sarcostyle D 
is stretched at an early phase of contraction, B is a relaxed 
sarcostyle slightly altered by endosmosis, sarcostyle A is swollen 
and beaded through the action of a hypotonic solution. 
In support of his claim that the striae are not reversed during 
contraction, Schaefer cites also the experiments of Macallum,” 
designed to determine the distribution of the potassium salts in 
the sarcoplasm during the several functional stages. Schaefer 
selects certain of Macallum’s figures of the wing-muscle sarco- 
styles of Dytiscus, and interprets these as demonstrating that 
also the potassium salts do not shift their position during con- 
traction, from their location within the dark disc in the relaxed 
sarcostyle. Schaefer would thus seem to identify the dark disc 
not only with the anisotropic stratum of Englemann, but also 
with the potassium-containing stratum of Macallum. An 
examination of these selected figures from Macallum’s paper 
(fig. 289 of Schaefer?’) reveals the fact, however, that the so-called 
contracted sarcostyles are actually only fibrils which have 
become artificially beaded through osmotic modification. These 
illustrations reveal only that the distribution of the potassium 
salts within the sarcoplasm is roughly coextensive with the dark 
dise, but give no information regarding this distribution during 
contraction. Reference to Macallum’s original work (p. 118) 
reveals, moreover, that the distribution of potassium salts in 
uncontracted and contracted muscles is not a very precise matter. 
In the uncontracted muscle the potassium is said to be generally 
limited to the dim band, but also the potassium reaction is most 
marked in those zones of the dim bands immediately adjacent 
to the light bands. The latter condition, in my opinion, is 
comparable with an early stage of contraction. In the con- 
tracted sarcostyle Macallum found the most marked reaction for 
potassium in the central regions of the dark disc. However, 
when the penetration of the reagent (the hexanitrite of cobalt 
and sodium) was delayed, the staining reaction revealed the 
potassium sometimes in the light discs and sometimes along the 
level of separation between the light and dark discs. 
