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समानस्तु द्वयोर्मध्ये गोक्षीरधवलप्रभः । आपाण्डर उदानश्च व्यानो ह्यर्चिसमप्रभः ॥
Prana is said to be blood-red, the colour of ruby or coral; apana is the colour of indra-gopa (an insect which is white or red in colour); samana is in-between the colour of pure milk and crystal (oily and shining), udana is apandara (pale white), and vyana is the colour oiarchis (a ray of light).
Union of prana and apana
Of the five pranas, the two most influential are prana and apana. The Shiva Samhita (3:6) states:
अत्रापि वायवः पंच मुख्याः स्युर्दशतः पुनः । तत्रापि श्रेष्ठकर्त्तारौ प्रानापानौ मयोदितौ ॥
Out of the ten (major and minor pranas), the first five are the leading ones; even among these, prana and apana are the highest agents.
Prana and apana are the two opposite forces in the physical body; prana moves upward from the navel and apana downward. Under the influence of apana, the consciousness is drawn down to mooladhara, which is associated with the earth element, the grossest level of manifestation. There it generates desires and interacts with the world. Under the influence of prana, the consciousness is drawn upward towards sahasrara, which is associated with ether, the subtlest element, and with the unmanifest dimension, where it experiences its higher nature.
In the practice of yoga the direction or movement of prana and apana are changed. The upward flow of prana is directed downward and the downward flow of apana is directed upwards. In this way they both move towards one another and meet at samana. At this meeting point the energy of yogagni, fire of yoga, arises. When these two aspects of life, the inner and the outer, the mundane and the spiritual are brought together and united, the kundalini awakens.
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