Charaka Samhita

Charaka Samhita is considered to be the most ancient and authoritative writing on ayurveda available today. It also explains the logic and philosophy on which this system of medicine is based. The detailed biography of the composer of this treatise—that is, sage Charaka—is not known to the posterity. Interestingly, it is not an original writing of a single person rather like all Vedic knowledge it is a continuation and renewal of that ancient knowledge system. In fact, Charaka had redacted the Agnivesa Samhita (an edited version of Atreya Samhita). The available form of Charaka Samhita was again worked upon by Drdhabala (living in about 400 AD) long after sage Charaka.
According to Charaka, science is dependent upon yukti—a quality of the intellect that enables it to perceive phenomena brought into existence by a multiplicity of causes. Thus, it's not surprising that much of the treatise of Charaka Samhita is in the form of a symposium wherein groups of ayurvedic scholars take up a series of topics for discussion. This gives indication that the science of ayurveda is a product of constant verification, fine-tuning and authentication by an active community of physicians. The samhita mentions about the gradual development of the fetus within the womb in minutes that equals the modern medical version in accuracy.
The language is Sanskrit and is written in verse form. The style is in keeping with the Vedic oral tradition of conserving knowledge. The samhita contains 8,400 metrical verses.
Charaka followed the Atreya School of Physicians, which predominantly deals with treatments through internal and external application of medicine. Though the samhita contains all the theoretical knowledge of ayurveda it's focus is on healing the body, mind and soul of a patient in the minimum invasive manner that's Kayachikitsa. Hence, he placed great emphasis on the diagnostic part of the treatment. So much so that he classified everything from solar calendar to topography to the timing of the birth of a child. He identified eight stages of a disease from its inception to the culmination. Charaka also laid great emphasis on the timing and manner of the collection of medicinal plants.
Charaka sought to correct the element of fire or the digestive function in a body. It sought to alter the chemical processes in the cells by purification methods and medicinal application. From a greater perspective Charaka laid emphasis for health and longevity to strike a balance between one's corporeal and spiritual being. That is the reason why Charaka went so detail into the diagnosis of a disease's origin.