Abstract
The fine structure of rabbit platelets prefixed in acetaldeyhde or paraformaldehyde is compared with that obtained after glutaraldehyde prefixation: osmium tetroxide post-fixation was used. Acetaldehyde prefixation causes platelets to swell, reduces the density of their matrix and causes a partial loss of the external platelet coat. Within the cytoplasm, very dense granules and microtubules are not seen; other organelles are preserved and the vacuolar system becomes very prominent. Platelets prefixed in paraformaldehyde are rounded. Their matrix is not very dense and their membranes are not well preserved. The number of very dense granules is reduced and microtubules are not seen. Other cytoplasmic organelles are preserved.
Cytoplasmic microfibrillae may be seen after either acetaldehyde or paraformaldehyde prefixation but not after glutaraldehyde fixation. Apart from this, glutaraldehyde/osmium tetroxide fixation preserves platelet shape and ultra-structure best.