What are the types of fixatives?

Fixatives may be classified into three types based on their chemical composition, type of structures fixed, and number of structures fixed. 

Based on chemical composition, fixatives may be classified as: 

1. Physical agents – Heat and microwaves 
2. Oxidizing agents – Osmium tetroxide
3. Aldehydes – Formaldehyde, glutaraldehyde, acrolein
4. Coagulants – Acetic acid, ethyl alcohol, methyl alcohol, 
5. Miscellaneous – Mercuric acid, picric acid

Based on types of structures fixed, fixatives may be classified as: 

1. Cytologic fixatives – Clarke’s fluid, Flemming’s fluid, glacial acetic acid
2. Histochemical fixatives – Formaldehyde, glutaraldehyde, vapor fixatives
3. Microanatomical fixatives – Helly’s fluid, Bouin’s fluid, Heidenhain’s fluid, 

Based on number of structures fixed, fixatives may be classified as: 

1. Simple fixatives – Formaldehyde, picric acid, osmium tetroxide
2. Compound fixatives – Zenker’s fluid, Bouin’s fluid, formol saline