Carnoys

Carnoy's solution, also known as Carnoy's fixative, is a rapid precipitating fixative used in histology and cytology. It penetrates quickly and preserves cellular detail, especially nuclear and chromatin structures, making it useful for preparing slides for chromosome studies and other nuclear analyses. The classic formulation consists of 60% ethanol (or, in some variants, methanol), 30% chloroform, and 10% glacial acetic acid by volume. Variations exist that modify the alcohol type or the acetic acid proportion, all aiming to achieve fast fixation with good nuclear preservation.

Preparation and use involve making the fixative fresh and immersing specimens for a short period, followed by standard rinsing and processing for staining. It is commonly employed for cytology smears and for preliminary fixation of tissues prior to further processing, including staining with methods such as Giemsa to visualize chromosomes and nuclear detail.

Advantages of Carnoy's solution include excellent preservation of nuclear morphology, rapid fixation, and strong staining of chromatin. However, there are notable limitations and hazards. The formulation contains chloroform and acetic acid, which are toxic and corrosive; it can cause tissue distortion and shrinkage and may alter certain chemical components, affecting downstream immunohistochemical or molecular analyses. Because of these concerns, its use may be restricted or followed by alternative fixatives depending on the target application.

Safety and handling require ventilation, protective equipment, and proper disposal in accordance with institutional and regulatory guidelines. While still in use for specific cytological and chromatin-preservation protocols, many laboratories rely on other fixatives for routine histology or for antigen preservation.