Neutrophils (heterophils in some teleosts) are the primary, most motile granulocytic white blood cells that act as first responders in acute inflammation, rapidly migrating via chemotaxis to the site of infection within minutes to hours to phagocytose pathogens and release reactive oxygen species (ROS).

10% Neutral Buffered Formalin (approx. 4% formaldehyde solution buffered to pH 7.2–7.4) is the universal, most widely utilized histological fixative. It cross-links amino groups of structural proteins to preserve tissue architecture and cellular morphology.

Gram's staining, developed by Christian Gram in 1884, is the fundamental differential staining technique used in bacteriology to categorize bacterial cultures into Gram-positive (retaining crystal violet) and Gram-negative (counterstained pink by safranin) based on cell wall peptidoglycan thickness.

In veterinary pathology:
Atrophy: Reduction in size and/or cell number of a previously normal, fully developed organ or tissue due to nutrient starvation, disuse, or disease.
Hypertrophy: Increase in the size of cells resulting in enlarged organ size.
Aplasia: Failure of an organ to develop completely during embryogenesis.