1. The acetalphosphatides which are the precursors of the aldehydes (‘plasmal’) responsible for Feulgen's plasmal reaction are extremely labile compounds which hydrolyse very rapidly in acid media, and are destroyed more or less rapidly during fixation. The liberation of aldehydes from them is catalysed by mercuric chloride.
2. Ordinary unsaturated lipoids, if exposed to air, become capable of producing a colour with Schiff's reagent, which, unless a control section is used, can be misinterpreted as a positive result for Feulgen's plasmal reaction. Mercuric chloride has little or no influence over the oxidative rancidity of unsaturated lipoids.
3. Any technique prescribed for showing the plasmal reaction must avoid acid media and prolonged fixation and handling of the tissues. A control section is a necessity.