A novel optical channel processing unit is disclosed that is useful for multiplexing, demultiplexing and switching optical signals in a WDM network. Means include a heat pipe configuration comprising at least one heat conduit in thermal communication with a heat flux sensor and a surface of a living body. Compared with analog compensation with an external storage capacitor, temporal drift effects do not distort the offset compensation on the differential 10 amplifier. Gargling with the composition is effective in relieving sore throats and minor throat irritations.