In the previous paper, the author reported that the basophilic substance of cytoplasm contains a quantity of lipid which attaches perpendicular to the long axis of fibrous protein in cytoplasm. In this chapter, the author aimed to prove histochemically the lipid in cytoplasmic basophilia and to analyze the unmasking mechanism of the so-called "masked lipid" on various cells including. By means of Sudan black B (SBB) staining, the lipids independent of cytoplasmic organella proved to exist in liver cells and some other cells that can be removed by the treatment with ether-alcohol. The lipids belonging to basophilic organella cannot be removed by this treatment. Usually, these lipids remained through ether-alcohol treatment showing the characteristics of the so-called "masked lipid", which does not show affinity for SBB at all in the smeared, dried and fixed preparation. These masked lipids were unmasked by the action of M/10 trichlor acetic acid for 30 to 60 minutes at 50°C and then stained by SBB. Through this treatment with trichlor acetic acid, cytoplasm and nucleus did not lose their basophilicity. The action of RNase also resulted in an unmasking effect but the effect is very slight. Therefore, unmasking mechanism of trichlor acetic acid is not related to the decomposition of nucleic acid. The various managements of smeared specimen before the treatment of the same but with trichlor acetic acid have an important effect upon the unmasking effect of trichlor acetic acid and RNAase, i. e. the drying followed by formalin vapor or methanol fixation inhibited markedly the unmasking effect of trichlor acetic acid. On the contrary, the basophilia of cells fixed without drying showed a strong affinity for SBB. This fact may indicate that the lipid in living cells should be an unmasked state, and in most parts of the so called "masked lipids" masking schuld be resulted artificially by drying of living cells. The lipids in the cytoplasmic organella in the cells of dried and fixed specimen or paraffin sectioned preparations by routine method showed a marked resistance for their extraction with ether-alcohol. In the case of freez-dried section, however, the lipids in cells disappeared immediately after the action of organic solvent and lose their affinity for SBB. From these resluts, the author concluded that the so-called "masked lipid" should be loosely combined with basophilia in living cells, and drying and fixation should result in a strong binding between lipids and organella, especially drying process results in a remarkable masking effect.