In India, places such as Takshila and Varanasi emerged as centers of medicine and learning. Charak Samhita by Charak and Sushrut Samhita by Sushruta is the two important texts in this field. In the court of Kanishka, Charak was the Raj Vaidya (royal doctor). He is credited as the first person who talks about digestion, metabolism, and immunity. He also knew the concepts of Genetics.