The main concentration of the book is to present an analysis of "Caraka Samhita", the crucial source book on Indian medicine. According to Chattopadhyaya, "discarding scripture orientation, they Indian physicians insist on the supreme importance of direct observation of natural phenomena and on the technique of rational processing of the empirical data. They go even to the extent of claiming that the truth of any conclusion thus arrived at is to be tested ultimately by the criterion of practice". For them, "everything in nature occurs according to some immutable laws, the body of which is usually called svabhava in Indian thought" and "from the medical viewpoint there can be nothing which is not made of matter". They even say that "a substance is called conscious when it is endowed with the sense-organs". Further, Chattopadhyaya shows: