About the practice of drawing the up-going and the down-going air together at the Navel Center, one important point should be mentioned: some say the yogi should visualize the whole body full of Prana; some say the Prana should be visualized only full above the Heart Center or above the Throat Center. These instructions are unsound--because the true and sound teaching is to visualize the small Ah word whereupon the two pranas unite [**]. There

are two reasons for this. First, through leading the Prana into the Central Channel, the Life-Prana and the down-going prana are unified. Second, through visualizing words, the essential mental concentration process is automatically completed. Furthermore, whenever the mouth of Ro-ma and Rkyang-ma are open, the mouth of the Central Channel is closed and vice versa.

Through the practice of Vase-Breathing, the out-going breathing from the Ro-ma and Rkyang-ma is stopped; and through visualizing the air entering into the Central Channel, the yogi eventually will be able actually to lead the incoming air into the Central Channel.

The manner and the duration of holding the breath are explained by Pag-mo-grub-pa as follows: In the beginning stage, practice on taming the nerves is emphasized. The yogi should not hold his breath to the point of strain. The yogi should hold the breath easily and not for too long. Gradually, he should increase the duration of the holding period. Until the breath becomes very smooth and submissive, he should not engage in the stronger breathing practices, such as shaking the upper part of the body and forcibly pulling up the prana. He should release his breath before he feels uncomfortable, and not try to hold it too long. Even if he tries to do so, it will not help the gathering of pranas in the Central Channel, for the prana will remain in the Transformation Wheel only a moment and then go outside. Although to hold the prana outside the Wheel Center for a long period will produce a little warmness and bliss, it does not help the prana to enter into the Central Channel.

In the practice of visualization, the yogi tries to visualize the subject clearly, but a clear image appears in his