Srimad Bhagavatam Canto-03, Chapter-26, Text-41
rasa-matram abhut tasmad
ambho jihva rasa-grahah
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
By the interaction of fire and the visual sensation, the subtle element taste evolves under a superior arrangement. From taste, water is produced, and the tongue, which perceives taste, is also manifested.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
The tongue is described here as the instrument for acquiring knowledge of taste. Because taste is a product of water, there is always saliva on the tongue.
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