Final answer:
The adage 'One night with Venus, the rest of your life with Mercury' associates a short-lived romantic encounter with the lifelong treatment of the disease syphilis using mercury, due to its historical treatment regimen.
Step-by-step explanation:
The old adage 'One night with Venus, the rest of your life with Mercury' refers to the treatment of a disease that was historically associated with romantic or sexual encounters, specifically syphilis. In ancient times, 'Venus' was used as a symbol for love and beauty, and by extension, sexual contact. However, syphilis, a sexually transmitted disease that was widespread and incurable before modern antibiotics, was treated with mercury, often for the remainder of the patient's life. Mercury treatment was known for its severe side effects and questionable efficacy. Therefore, the adage reflects the regret of a fleeting moment of pleasure leading to a lifetime of suffering due to the disease.