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=== Introduction ===

=== Introduction ===

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Important principles of diseases in this section of the ''Roga Chatushka'' (tetrad on diseases) have been described. The preceding chapter provided a broader explanation for the cause of innumerable diseases due to ''dosha'' vitiation as well as variations in characteristics like pain, sign, etiology, site of origin, site of manifestation, symptoms and nomenclature. However, only the most important diseases, probably prevalent at that time, have been classified in view of prescribing treatment. Classification of these known diseases, based on characteristics provided above, and coupled with a few more variables such as prognosis, chronicity, treatment etc. have been done at various places within the [[Charaka Samhita]]. On critically analyzing, we find that the diseases have been classified into groups having as few as one to as many as eight diseases each.Three disease groups of twenty types each have been classified at the end. It has been observed that the listing of groups by diseases has been done in a descending order - from those having eight diseases to one  - because there are no other groups that have greater than eight types of diseases within them, except for the three groups with twenty types. Hence, these outliers (with twenty types) have been enumerated at the end rather than in the beginning of the chapter. Even though there are eighteen types of obstinate skin diseases, only the seven most obstinate ones have been enumerated here.  

Important principles of diseases in this section of the ''Roga Chatushka'' (tetrad on diseases) have been described. The preceding chapter provided a broader explanation for the cause of innumerable diseases due to ''dosha'' vitiation as well as variations in characteristics like pain, sign, etiology, site of origin, site of manifestation, symptoms and nomenclature. However, only the most important diseases, probably prevalent at that time, have been classified in view of prescribing treatment. Classification of these known diseases, based on characteristics provided above, and coupled with a few more variables such as prognosis, chronicity, treatment etc. have been done at various places within the [[Charak Samhita]]. On critically analyzing, we find that the diseases have been classified into groups having as few as one to as many as eight diseases each.Three disease groups of twenty types each have been classified at the end. It has been observed that the listing of groups by diseases has been done in a descending order - from those having eight diseases to one  - because there are no other groups that have greater than eight types of diseases within them, except for the three groups with twenty types. Hence, these outliers (with twenty types) have been enumerated at the end rather than in the beginning of the chapter. Even though there are eighteen types of obstinate skin diseases, only the seven most obstinate ones have been enumerated here.  

As mentioned above, various modes of classification have been used to classify diseases in the Samhita - some diseases have been classified only according to ''doshas'' involved, such as ''apasmara'' (epilepsy), ''akshi roga'' (eye diseases), ''mukha roga'' (diseases of oral cavity), ''pratishyaya'' (rhinitis) etc. In some cases, apart from ''doshas'', certain etiological factors have also been considered and nomenclature has been done accordingly e.g. in case of ''unmada, pandu roga, hridroga, chhardi, shosha, vrana'' etc. Some diseases have been classified taking into consideration only prominent clinical features, such as in the case of ''kushtha, kilasa, arsha, jwara,'' and ''aayama''.  In some cases, nomenclature is based on the site involved in pathogenesis, as in ''rakta pitta, kamala'' etc, while in some cases, severity has been the basis for classification e.g. ''vatarakta''. We also find groups containing sub-classes or sub-groups of diseases. This hierarchical basis has been used while classifying the three disease families mentioned that have twenty types of diseases. ''Krimi'' are first classified into ''bahya, raktaja, shleshmaja'' and ''purishaja'' which are sub-classified into other diseases. Similarly, twenty types of ''pramehas'' are broadly classified into three groups on the basis of ''doshas'' and then subtypes are mentioned. ''Yoni vyapada'' (gynecological disorders) are broadly classified into diseases caused by ''dosha'' and diseases caused by amalgamation of ''doshas'' and ''dushyas'', with further sub-classifications. Thus, it can be said that classification has not been restricted to a single hierarchic pattern but a hierarchical system for disease classification as well. Still, the classification of all known diseases is not complete using the above mentioned system. Need-based or contextual re-classification of various disease groups can be found in many places within the Samhita.  

As mentioned above, various modes of classification have been used to classify diseases in the Samhita - some diseases have been classified only according to ''doshas'' involved, such as ''apasmara'' (epilepsy), ''akshi roga'' (eye diseases), ''mukha roga'' (diseases of oral cavity), ''pratishyaya'' (rhinitis) etc. In some cases, apart from ''doshas'', certain etiological factors have also been considered and nomenclature has been done accordingly e.g. in case of ''unmada, pandu roga, hridroga, chhardi, shosha, vrana'' etc. Some diseases have been classified taking into consideration only prominent clinical features, such as in the case of ''kushtha, kilasa, arsha, jwara,'' and ''aayama''.  In some cases, nomenclature is based on the site involved in pathogenesis, as in ''rakta pitta, kamala'' etc, while in some cases, severity has been the basis for classification e.g. ''vatarakta''. We also find groups containing sub-classes or sub-groups of diseases. This hierarchical basis has been used while classifying the three disease families mentioned that have twenty types of diseases. ''Krimi'' are first classified into ''bahya, raktaja, shleshmaja'' and ''purishaja'' which are sub-classified into other diseases. Similarly, twenty types of ''pramehas'' are broadly classified into three groups on the basis of ''doshas'' and then subtypes are mentioned. ''Yoni vyapada'' (gynecological disorders) are broadly classified into diseases caused by ''dosha'' and diseases caused by amalgamation of ''doshas'' and ''dushyas'', with further sub-classifications. Thus, it can be said that classification has not been restricted to a single hierarchic pattern but a hierarchical system for disease classification as well. Still, the classification of all known diseases is not complete using the above mentioned system. Need-based or contextual re-classification of various disease groups can be found in many places within the Samhita.