1. When the testis of Acheta domesticus is fixed in Flemming's fluid and embedded in gelatine, Sudan black reveals scarcely any lipid in the externum of the acroblast.
2. It can be shown that the externum of the acroblast contains much lipid in a masked (bound) form.
3. Experiments were performed to find what substances were effective, after Flemming fixation, in unmasking the lipid of the externum and thus making it colourable by Sudan black.
4. The following substances were found to act as unmasking agents: ethanol, dioxane, phenol, resorcinol, hydroquinone, pyrogallol, tannic acid.
5. Under the conditions of the experiment, the most effective unmasking agents were 90% ethanol and 5% hydroquinone.
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