Ras Rasayan

Rasāyana , रसायन is a Sanskrit word, with the literal meaning: Path (āyana) of essence (rasa). It is a term that in early ayurvedic medicine means the science of lengthening lifespan, and in later (post 8th-century) works sometimes refers to Indian alchemy.
Rasa (Rus) in Sanskrit means juice, essence, emotion etc and ayana means path. Therefore rasayana roughly translates to - The path of the juice. Rasa (Rus) nourishes body, boosts immunity and helps to keep the body and mind in best of health. The main aim of Ayurvedic rejuvenation therapy or rasayana therapy is to restore spirit and vitality and thereby attain longevity. 
The concept of Rasayana is based on these two principles of conservation and transmutation of energy.Rasayana therapy strives to improve physical, mental and moral Qualities. It prevents old age, restores youthfulness, improves the complexion and the voice, increases physical strength and immunity. It strengthens memory and intelligence, gives happiness to oneself, and a life which is beneficial to others .
Benefits of Rasayana -: 
To increase body tissues * To increase digestive power * To increase the metabolic process at a tissue level or to improve endocrine gland function * To remove waste products or to remove excess tissues in the body * To increase the functional capacity of the brain * To increase the strength and immunity of the body * To destroy disease and establish homeostasis of energy, which prevents early aging.