The evil spirit by whose influence men are always persiented by the Pishachas and thus turn mad is called the Pishacha spirit.
अधिरोहन्ति यं नित्यं पिशाचा: पुरुषं प्रति। उन्माद्यति स तु क्षिप्रं ग्रहः पैशाच एव सः॥