Fig. 2. Histochemistry and immunohistochemistry on a composition of masseter (m) and longissimus dorsi (Ld) (a–c) and on a sample of red semitendinosus (Str) (d–f). Consecutive sections were stained for mATPase with acid (pH 4.55; a) or alkali (pH 10.3; d) preincubation and with monoclonal antibodies specific for MHC-2A (SC71; b,e) and MHC-2X (BF-35; c,f). Slow fibres (type1) are dark with mATPase staining after acid preincubation and white after alkali preincubation. In masseter, only type 1 and 2A are present, whereas in red semitendinosus type 2X and 2A/X fibres are also detectable. In Ld muscle, the conventional 2B fibre type (2^*) might be either 2B or 2X or hybrids (2A/X or 2X/B). Scale bars, 40 µm.