This section is from the book "The Sushruta Samhita", by Kaviraj Kunja Lal Bhishagratna. Also available from Amazon: The Sushruta Samhita.
A Deva Graha strikes i. e. possesses a man at full moon ; an Asura Graha at the meeting of day and night i. e. in the morning and evening twilights ; a Gandharva generally on the eighth and a Yaksha on the first day of the fortnights. A Pitri Graha possesses a man on the new moon day ; and a Sarpa Graha (serpent-devil) enters on the fifth day of the new or full moon. A Rakshasa Graha possesses a man at night and a Pis'acha Graha on the fourteenth day of the fortnights. A Graha imperceptibly enters into the body of the patient in the same way as an image imperceptibly enters into (the surface of) a mirror, as heat or cold penetrates into the body of an organic being and as the rays of the sun are collected in the crystal lens known as the Surja-kanta gem and as soul enters the body unseen. I 5-16.
* In place of
Madhava reads
i. e. (it is also incurable) when it has continued for thirteen years.
Austere penances and vows, self-control, truthfulness, charities and religious practices as well as the eight qualities* are either wholly or partially present in the Grahas according to the degree of their respective power. These spiritual bodies never come in contact with, nor do they themselves strike human beings. Those who hold contrary opinion, must be ignorant of the mysteries of demonology. It is the thousands and hundreds of thousands and hundreds of millions of the followers of the Grahas, who are fierce-looking and fond of flesh and blood, and who stir abroad in the night and possess the men on earth. 17.
Of these malignant spirits (Grahas) those who are associated with the gods should be regarded as of celestial essence in virtue of their partaking of a tinge of divine virtues. Those who are known as Deva Grahas and are cleanly should be worshipped and homaged and prayed like the other gods of our Pantheon. The Grahas should be credited with those powers, virtues and characteristics which are the attributes of their respective masters. They are the issues of Nairiti's daughters and their living has been fixed as such by the various Ganas (or groups of gods and demi-gods) as they are always adverse to truthfulness, i. c. the true performance of the dictates of the Sas'tra. Those that roam about in quest of evil and mischief in spite of the celestial nature of their own divine essence and temperament have been termed Bhutas (spirits). Hence that branch of medical science which treats of the therapeutics of diseases which originate from the influences of Bhutas (or Grahas) is called the Bhuta-Vidya. 18-20.
(1) Amman or the superhuman power of becoming as small as an atom at will. (2) Laghiman - power of becoming excessively light at will. (3) Vyapli - expansiveness. (4) Pra-kamya - irrisestible will. (5) Mahiman - power of increasing the size at will. (6) Is'itva - greatness. (7) Vas'itva - self-control and (8) Kamava-sayita - suppression of passion.
 
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