4 H. E. JORDAN 
calated dises, which I am now able to demonstrate also in human 
leg muscle,’ are essentially modified irreversible contraction 
bands. But Schaefer claims that a contraction band is an 
optical illusion. This claim is based chiefly upon his description 
of an alleged contracted sarcostyle of wasp’s wing muscle treated 
with Rollet’s gold-chlorid technic. It became necessary, there- 
fore, in the interests of my interpretation of intercalated discs, 
to reinvestigate wasp’s wing muscle. A comparative study of 
the sarcostyle of this muscle after treatment with Rollet’s and 
other technics, has convinced me that. what Schaefer describes 
as a functionally contracted sarcostyle is in fact one that has 
become swollen and in consequence shortened; that is, one 
artificially contracted, through the action chiefly of the acidu- 
lated hypotonic (formic-acid-water) solution employed in Rol- 
iet’s technic. In a functionally contracted sarcostyle of this 
wing muscle, as in insect leg muscle and other striped muscle 
generally, there occurs a genuine reversal of striations during 
contraction as regards a darker colored and more deeply staining 
constituent of the ‘dim’ disc. 
It may be stated at once that there is no absolutely definite 
correspondence between the distribution of the anisotropic con- 
stituents of the sarcoplasm and the limits of the deeply staining 
substance of the dark discs at the different functional phases. 
An unstained fiber appears striped, not because the anisotropic 
material is segregated into definite narrow strata (discs), but 
because of a chemically different, as demonstrated chiefly by a 
difference of staining reaction, and a darker sarcoplasmic con- 
stituent segregated in the darker ‘bands.’ ‘This same substance, 
not a specific anisotropic substance, stains deeply in basic dyes 
and gives to microscopic preparations, as compared with living 
material, a similarly transversely banded appearance. In the 
following pages attention will be directed primarily to the be- 
havior of this substance during contraction, and to its relation 
to the formation of intercalated discs. 
