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XII] The Theory of Rasas and their Chemistry 365 (in the modern sense) of medicines on human organs were known, the most obvious way in which the medical effects of herbs, roots, etc. could be classified was on the basis of taste, and by Caraka and Susruta we are told the effects of the different rasas on the different morbidities of the body, vāyu, pitta and kapha. As the main source of all diseases was unequal increase or decrease of vāyu, pitta and kapha, a classification which described the rasas in such a way that one could know which rasa increased or decreased which of the morbidities was particularly useful. But it is obvious that such a classification, though simple, could not be universally true; for, though the taste is some indication of the medicinal property of any substance, it is not an infallible one. But no other mode of classification was known; it was supposed that the taste (rasa) of some substances changed altogether after digestion and that in such cases the taste which changed after digestion (pāka) would be operative. Cakrapāņi says that in those cases where the taste on the tongue (rasa) agrees with the taste as produced after the digestive process, the effect in that direction becomes very strong, but in the case where the latter differs from the former the operation of rasa becomes naturally weak because the force of the taste produced by the final operation of the digestive process is naturally strong?. Caraka thought that there were only three rasas as the result of digestion, viz. kațu, madhura and amla; Susruta rejected the last, as has already been described. But even this was not sufficient; for there were many other effects of medicine which could not be explained on the above suppositions. In explaining this, the theory of virya was introduced. In addition to taste substances were considered to possess other properties of heat and cold, as judged by inference, tactual properties of slipperiness, movement, moisture and dryness, etc., sharpness, etc. as manifested by odour, and these were supposed to produce effects in supersession of rasa and vipāka. It was only in the cases where no sensible data of any kind could be found to indicate the medical properties of the thing that the idea of prabhāva was introduced. The chapters in Ayur-veda on dravya
1 Cakrapāņi on Caraka, 1. 26. 65. Cakrapāņi points out that the hot (kațu) taste is at first useful in cleaning the phlegm of the throat, but, since it becomes sweet after digestion, it acts as a nutrient (vrsya). But, except in the case of such local actions, it is difficult to understand why the rasa which was altered by digestion should have any such effect as Cakrapāņi suggests (viparyaye tu durbalam iti jñeyam).
