In histological specimen the vesicles of air and particles of dye are seen, which are not typical for this specimen. What is it?

In histological specimen the vesicles of air and particles of dye are seen, which are not typical for this specimen. What is it?

1.  Angstrom unit


2.  Exocytosis


3.  Clasmatosis


4.  Invasion

*Artefact