The great teacher of Kaya-cikitsita or medicine is Kisna Atreya according to the Mahabharata.
The Caraka Samhita, the greatest of the works on medicine purports to be the final embodiment of Atreya�s teaching. Every chapter opens with the words �Thus spake the worshipful Atreya".
Agnivesa and other disciples are greatly attached to him and hold him in supreme veneration. He is the first systematic teacher of the science of medicine after it was brought from Indra and imparted to the noble galaxy of sages by Bharadwaja.
The Caraka Samhita does not say explicitly that Atreya learnt the science from Bharadwaja, but it just mentions that Bharadwaja, having brought the sacred wisdom from Indra, imparted it to the sages Marlci and others, among whom Atreya is one. We are then introduced to a situation wherein Atreya, the compassionate one, taught this holy science of life to his disciples for the ultimate benefit of all creatures.
Despite the absence of a specific mention of the transmission of the science from Bharadwaja to Atreya, the fact implied is so transparent that the authors omitted the statement of the obvious. The verse,opening with the word 'thus� is meant to convey this fact viz, in the manner foregone i e the sages including Atreya having learnt the science, then it so happened, that Atreya began teaching medicine to his disciples. Cakrapini, the commentator, is emphatic on this point and contradicts the conclusion of some identifying this Atreya with Bharadwaja who learnt the Ayurveda from Indra. For the latter, mistake is made by some in view of the description in Caraka in the chapter on Rasayana, where Atri is said to have received the knowledge directly from Indra, That pertains only to Rasayana and on a later occasion than the one described in the opening chapter and therefore does not apply to the question of the whole science of Ayurveda-as it- was taught by Indra to Bharadwaja and again by him to the sages of whom Atreya is one.
In this connection it is interesting to note that Vagbhata and Bhavamisra refer to Punarvasu or the son of Atri as approaching Indra at the head of a group of sages and learning the Scienceof medicine from him.
That this Atreya is one of the great sages, expert in the sciences and spiritual knowledge and one held in high esteem is evident from the prefixed title to his name �Bhagawan'. This is a title that only the very greatest of sages of supreme spiri�tual attainment may hope to obtain. The qualifications or merits that entitle one to this honour are set forth thus.
'�He is to be known as �Bhagawan' who is possessed of the knowledge of creation and dissolution of the world and of the birth and death of creatures and also of science both material and spiritual."
Atreya was thus among the elite of the sages, adept in all the sciences and mature in spiritual wisdom and a teacher especially of the science of medicine. Though versed in all the eight branches of the Science of Life he devoted this treatise entirely to medicine and referred his disciples to other teachers and treatises when resort to surgical and other special procedures were in demand.
"This is the domain of the surgeons", is a remark one meets with when there are indications for surgical remedies.
�We do not attempt to expatiate on them here, as that belongs to the province of specialists.�
Thus Atreya is a specialist in Medicine (�Kaya-Cikitsa�) and specially therapeutics and a popular verse in vogue assigns excellence in each department of medicine to each one of the four expert teachers and writers on the medical science.
�Madbava is unrivalled in diagnosis, Vagbhata in general principles of medicine, Susruta in surgery and Caraka in therapeutics.�
Atreya is also known as Punarvasu or Punarvasu Atreya. In the Caraka Samhita, the word Punarvasu is used as a synonym for Atreya. The opening line of every chapter contains always the words �thus spake the worshipful Atreya�� and at the end of the chapter in the recapitulation of the subject of the chapter sometimes other synonyms like Punarvasu, the great sage, Candrabhaga or Krsna Atreya are used, thus making it clear that Bhagawan Atreya was also known by his other names.
It is possible that the epithet Punarvasu may be signi�ficant of Atreya being born during the dominance of the constellation of that name. Such method of nomenclature we find at-many places in those days e. g. warrior Arjuna of the Pandavas was also called Phalguna from the constellation of that name under the influence of which he was born.
According to the Caraka Samhita, Atreya is the son of Atri for in many places he is refened to as the son of Atri. Though the term Atreya might apply either to the son of Atri or his near or distant descendants or to a disciple of Atri or even to one of the clan of Atri, yet as he is referred to as the son of Atri specifically, and also in view of the early times to which the situation pertains, it may be fairly concluded that the Atreya we are concerned with, is the direct son of Atri.
We find that in later days the royal physician of Sri Harsa was known as Rasayana Paunarvasava.This appellation of his may mean that he was either a descendant of Punarvasu, or one versed in the science of medicine propounded by Punarvasu. Considering that those versed in surgery were known as Dhanvantariyas, Dhanvantari being the first propounder of the Science, it is probable to conclude that the experts in the science of medicine propounded by Punarvasu were known as Paunarvasavas.