Additive - Coagulant
Fixing Agents
Any chemical which can preserve the structure or chemical composition of animal or plant tissues is considered to be a fixing agent. In order to accomplish this preservation, fixing agents are primarily effective against the proteins in the tissue. In some way each agent must denature, or chemically alter, these proteins. In the process the individual agents may, or may not, combine with the proteins (or other tissue components). Likewise they may, or may not, precipitate (or coagulate) the proteins as a consequence of their fixing action.
Agents which combine with proteins are called additive, and those which do not are called non-additive. Agents which precipitate proteins are called coagulant, and those which do not are called non-coagulant.
By combining these characteristics it is possible to classify fixing agents into four groups:–
The terms coagulant and precipitant are synonymous in this context as they both refer to precipitation of proteins and coagulation of protein gels.
| Fixing agent | Additive | Coagulant |
| Acetic acid | No | No |
| Acetone | No | Yes |
| Chromium trioxide | Yes | Yes |
| Ethanol | No | Yes |
| Formaldehyde | Yes | No |
| Glutaraldehyde | Yes | No |
| Mercuric chloride | Yes | Yes |
| Methanol | No | Yes |
| Osmium tetroxide | Yes | No |
| Picric acid | Yes | Yes |
| Potassium dichromate | Yes | No |
| Trichloracetic acid | No | Yes |
Reference
Baker, John R., (1958)
Principles of biological microtechnique
Methuen, London, UK.
