The saiva siddhantha pre-occupation with man and his systems are very unique. While it is a philosophy in its beginning it progresses up more and more as a science. It systematically studies man in his each point of existence. It traces his basic bio-chemical basis to the higher physiological functions and still later to the psychological nature of man.
These knowledge cannot be equated with modern biochemistry or physiology. The ancient knowledges were based on speculation and empirical investigations were less likely to have happened. But there were descriptions about the methodologies of empirical validations in saiva siddhantha twxts. This is an indirect evidence of any empirical studies of the past over human body,like anatomy or physiology. Nevertheless we know that these studies have resulted in a large body of information which had bloomed into the glorious SIDDHA MEDICINE SYSTEM. The basic bio-chemical blocks are the earth, water, fire, air and sky. These byproducts that are called THATHVEEHA (by-principles). Let us see one by one. 1.earth: it gives rise to the body organs like bones, muscles, nerves, skin and hair. 2. water: it is present in the mucus, blood, semen, sweat and urine 3.fire: the fire is present in the form of heat over the head, eye, heart, abdomen and the body. 4.air: air is present in breath, cough, belch, hiccough, sneeze, yawning, laugh, flatus and body gas. 5.sky:the 10 NADIs come from it. They are situated in various body parts, Left nose(idagalai nadi), pingalai nadi(right nose), suzhumunai nadi(spine), gandhari nadi (eye), athi nadi(body), siguvai nadi(semen), alambudai ndi(ear), purudan(feet), sangini(throat), gugudhai(chest) .etc. The siddha doctor studies these nadi, air position, heat, water loading and the physical feeling over the body parts and comes to a diagnosis of the malfunction of the body parts. The avathai concepts we saw earlier comes handy in the diagnosis of illness.