Studies on the Characteristic Staining Action of Osmium Tetroxide for Neutral Fat

Abstract

For the recent clectronmicroscopy biological materials are fixed with osmium tetroxide in most cases and the study on the stainability of osmium is one of the fundamental studies on the biological applications of electronmicroscopy. Bahr studied the reductibity of various substances for osmium tetroxide, and reported that the reductibity of protein was very strong and that of fat was less; ribonucleic acid :almost lacked the ability. These results are incompatible with the histochemical assumption.
We consider that the characteristic stainability of osmium tetroxide for neutral fat is not only chemical, but also physical. Our experiments show that fine osmium pariticles in water are diffusible in mineral oil and animal fat, but those in oil or fat do not diffuse in water. The physical character of neutral fat is that it has not :hydrophilic radical, so that neutral fat disperses in water as a fat droplet. The :hydrophobic osmium particles diffuse and stabilize in oil or animal fat. The fine .osmium particles which are reducted in cell sap, diffuse in a fat droplet and are not washed out by water. Then, the electron scatering power of fat droplets is very strong, containing many osmium particles. On the other hand, the osmium particles, can not diffuse in masked lipids which are enveloped in a fine network of carbonchain, of proteins and protein micell, and these lipid layer are more transparent than the protein membrane.
Under this assumption, the electronmicrograph, or fine structure, of the fat droplet, lipoid particle, endoplasmic reticulum and myelin sheath is discussed.