Carnoy’s solution is one of the older fixatives you’ll find in histology, with first publication in the 1880’s by Jean Baptiste Carnoy, a Belgian cytologist. It is a non-aqueous fixative made up of ethanol, chloroform and acetic acid. It can’t be stored for a long period of time but can be useful for specific tissues that require a solution without water. It is also a very fast fixative, which can be put in the fridge to slow down fixation time when necessary to avoid over-hardening and shrinkage, which can be disadvantages of Carnoy’s. Being an alcoholic fixative, it is good for preserving glycogen and is used in RNA stains.
Outside of the traditional histology uses, Carnoy’s is also used as a topical treatment after surgical removal of keratocysts. The epithelial lining can be hard to get rid of so Carnoy’s is used as a type of chemical cauterization to cause necrosis of the tissue, preventing future recurrence of cysts.
Another non-aqueous fixative you will see is Clark’s solution or fluid, which is similar to Carnoy’s except that it does not have the chloroform. You might see this also described as modified Carnoy’s solution. Chloroform is removed here to reduce carcinogen risk. Clark’s is often used for cryostat sections because of its rapid fixation. Clark’s solution is also ideal for blood or chromosome smears.
B Carnoy. La Cellule, Les globules polaires de l'Ascaris clavata, 1887