rupa-matrad vikurvanat

 tejaso daiva-coditat

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.