Sthirata, or fortitude, is acquired by the practice of the mudra. The mudra dealt with in works of hathayoga are positions of the body. They are gymnastic, health-giving, and destructive of disease, and of death, such as the jaladhara and other mudra. They also preserve from injury by fire, water, or air. Bodily action and the health resulting therefrom react upon the mind, and by the union of a perfect mind and body siddhi is by their means attained. The Gheranda Sanghita describes a number of mudra, of which those of importance may be selected. In the celebrated yonimudra the yogi in siddhasana stops with his fingers the ears, eyes, nostrils, and mouth. He inhales pranavayu by kakinimudra, and unites it with apanavayu. Meditating in their order upon the six chakra, he arouses the sleeping Kulakundalini by the mantra "Hung Hangsah," and raises Her to the Sahasrara; then, deeming himself pervaded with the Shakti, and in blissful union (sanggama) with Shiva, he meditates upon himself, as by reason of that union Bliss itself and the Brahman. Ashvinimudra consists of the repeated contraction and expansion of the anus for the purpose of shodhana or of contraction to restrain the apana in Skatchakrabheda. Shaktichalana employs the latter mudra, which is repeated until vayu manifests in the sushumna. The process is accompanied by inhalation and the union of prana and apana whilst in siddhasana.