Fig. 3. Histochemistry and immunohistochemistry on longissimus dorsi muscle. Consecutive sections were stained for mATPase after acid (a) or alkali (d) preincubation and with four monoclonal antibodies specific for MHC isoforms (b,c,e,f). The typical organization of islets of slow fibres surrounded by fast fibres is visible. Among fast fibres, hybrid fibres 2A/X and 2X/B are very abundant, while only few pure 2A and 2X are present. In the deep portion of the muscle, next to multifidus lomborum muscle, some pure 2B fibres are detectable (indicated as B). Scale bars, 40 µm.