Cytological Fixation of Mitochondria by Acids

Abstract

CERTAIN acids have been found surprisingly effective for the cytological fixation of mitochondria in various tissues from mice. In some cases, 0.1 N hydrochloric acid has proved almost as satisfactory as Altmann's or Helly's fluid (see Fig. 1). Usually, small pieces of tissue are fixed for 18–20 hr. in the acid, washed for two or more hours in water, dehydrated, cleared and embedded in paraffin. The washing does not appear to be essential. Tissues may be dehydrated directly from the acid, starting with 50 per cent ethanol. Sections cut at 3 µ are stained by either Hirschler's hæmatoxylin or Metzner's acid fuchsin technique. With the latter, differentiation is so rapid that it is preferable to use a reagent containing half the usual amount of picric acid. With the hæmatoxylin method, staining is not always uniform. After hydrochloric acid fixation, the mitochondria may be demonstrated in the cells of the liver, intestinal epithelium, renal tubules and pancreatic acini. Other tissues have not yet been studied. The best results have been obtained with liver, the least satisfactory with pancreas. Nitric or sulphuric acid may be used in place of hydrochloric, but the fixation is not quite so good. Chromic, phosphoric, formic, acetic, oxalic and citric acids, potassium dihydrogen phosphate and potassium hydrogen phthalate are unsatisfactory. After acid fixation, there appears to be no advantage in postchroming the above tissues except, possibly, the pancreas. In the case of hydrochloric acid at least, the results are not improved by making the solution isotonic.