Studies of Paramecium caudatum by means of scanning electron microscope and projection X-ray microscope.

Samples of Paramecium caudatum are observed by means of a scanning electron microscope (SEM) and a projection X-ray microscope (XRM) with computer tomography (CT) function. The samples are fixed with two kinds of fixatives, glutaraldehyde and osmium-tetra oxide acid. After the fixation and replacement procedure with t-buthyl alcohol, the samples followed by a freeze drying, well retain their structures. Surface structures, cilia and microfibrillar systems including infraciliary lattice structures, are clearly depicted by SEM observation. On the other hand, XRM images give quite different information, namely, in the case of osmium oxide fixation, the structures of internal organelles like the macronucleus placed in the central part of cell body and trichocysts located under the cell membrane of a whole body are visible. In the case of glutaraldehyde fixation, the surface structures and internal structures are both visible but their image contrast is fairly weak. In order to examine toxicological effect, Paramecium caudatum samples treated in the environmental condition containing nano-particles of Ag (17 nm across) and Co-ferrite (300 nm across) are observed with results of certain morphological differences, namely, inner vacuoles increase in number and in volume in Co-ferrite treated cells as compared with Ag treated ones. But then, cilia-less areas increase on the surface of the body of Ag treated cells. In the case of Co-ferrite treated cells, cilia-less areas are not clearly detected. Whether these morphological differences observed in Ag and Co-ferrite treated cells are caused by the differences of materials or particle sizes remain to be examined in future.