The Compendium of Caraka 4.8.17_1

4.8.17_1

yathā --- nirmale vāsasi suparikalpite rañjanaṃ samuditaguṇamupanipātādeva rāgamabhinirvartayati, tadvat; yathā vā kṣīraṃ dadhnā 'abhiṣutamabhiṣavaṇādvihāya svabhāvamāpadyate dadhibhāvaṃ, śukraṃ tadvat//

Just as a dye endowed with full qualities produces color on a clean, properly prepared cloth the moment it falls upon it, so it is [here]; or just as milk, when curdled with curd, leaves behind its own nature through curdling and attains the state of curd, so it is with the semen.