Quantitative histochemical investigations of semipermeable membrane techniques for the assay of acid phosphatase in skeletal muscle. II. Non-specific reactions in control sections.

The absorbances of skeletal muscle fibres at 530 nm in control sections of either fresh or boiled tissue, incubated according to Meijer's semipermeable membrane technique for acid phosphatase, increase linearly with incubation time. Moreover, the absorbances continue to increase even after the incubation has been terminated by immersion of the sections in formalin. The comparatively weakly absorbing yellow reaction product originally formed is transformed with 24 h of mounting the sections into a strongly absorbing purple material with an absorption maximum at 570 nm. The original yellow product seems to be hexazotised Pararosanaline adsorbed onto tissue proteins. The formation of the purple product can be prevented by treating control sections immediately after incubation with 70% ethanol for 30 min at room temperature in place of formalin. Ethanol stabilises the yellow non-specific reaction product but does not extract it from tissue sections. The ethanol treatment thus seems useful for improving the validity of Meijer's technique.