Agni mahabhoota :

The agni mahabhoota, which evolves next, from vayu mahabhoota, has vision (roopa) as its sense attribute and warmth (ushnatwa) as its main property. Now we have the privilege of viewing the creation! living beings, agni mahabhoota is the major constituent of biological humor pittadosha. The concept of agni is very peculiar to Ayurved. It is responsible for biotransformation. This agni provides the energy necessary for all activities in our body.  We know that, the energy can neither be created nor destroyed, but it can be changed from one form to another. We derive energy from the food we eat. Biological agni transforms the energy in the food to the energy, which can be utilised by our cells. The vitamins, minerals, carbohydrates, fats etc. we eat, are bio-transformed by this agni to the bodily substances. As long as this agni is proper, all the activities in body are carried out smoothly. Any disturbance in this agni causes imbalance in the homeostasis (equilibrium) and disturbs physiology. Entire Ayurvedic therapeutics is based on this concept of agni. In fact the branch of Ayurved, which deals with internal medicine and treatment, is called "kayachikitsa", where kaya means agni and chikitsa means treatment. We can appreciate that, Ayurvedic therapeutics devotes to correction and maintenance of biological agni. I would like to mention here that, contrary to the popular beliefs, anything herbal which is herbal cannot naturally become Ayurvedic medicine, but only the therapy, which considers the above mentioned concepts of Ayurved qualifies to be called as Ayurvedic medicine.