Analysis of the reflex behaviour of striped muscles involves data drawn from their histological structure, and the present observations deal with the differences in microscopical and macroscopical structure of muscles of different contractile properties. Stefano Lorenzini (55) mentioned the striking difference in colour between certain muscles of the limb in the rabbit as long ago as 1678. The classic investigations of Ranvier (63, 64, 65, 66, 67, 68), however, revealed most of the present knowledge of red and pale muscle. He showed that this redness was associated with slowness of contraction, and with the genesis of tetanus at lower rates of stimulus. Moreover, these functional differences were shown to be associated with a difference in histological structure, a relatively larger amount of granular sarcoplasm and more distinct longitudinal striation in the case of red muscle. Later studies (1, 57, 43, 72, 49) revealed the occurrence of these granular and longitudinally striated fibres in muscles in many species, and also that these fibres were not always associated with redness of pigmentation (57). The histology of muscle in the higher mammalian forms has shown that both granular “sarcoplasmic” and clear “aplasmic” fibres occur side by side in the same muscle, and these two types of fibre have been homologised with the red pale muscles of the rabbit (29, 30, 43, 73, 42).
EFFECTS OF SOME ISOTHIOUREA AND GUANIDINE SALTS ON VARIOUS PREPARATIONS OF SMOOTH AND STRIPED MUSCLE
