The Blessed Buddha once said:
In this some recluse or priest by means
of alert energetic effort and
enthusiasm,
through proper rational attention & concentrated focus reaches
absorption on
this sole thought: In this foul body of disgusting things
enclosed by skin, there are
head & body hairs, nails, teeth, skin, flesh,
sinews, bones, marrow, kidneys, heart,
liver, pleura, spleen, lungs,
mesentery, intestines, stomach, excrement, bile, lymph,
pus, blood,
sweat, fat, tears, tallow, spittle, snot, urine & joint-fluid... This is the first attainment of Vision...
Empty Frame: Having done this and gone beyond it, he
regards & perceives any body,
own or others, only as a chained frame of bones covered with flesh, vessels, fat & skin.
This is the second attainment of Vision...
Chain of Moments: Having done this & gone further, he
comes to understand & directly
experience this continuous sequence of discrete conscious moments
established &
manifesting both in this world and the other worlds.
This is the third attainment of Vision...
Continuous yet not Established: Finally, having done this & gone even
further than
beyond that, he comes to
understand & directly experience this unbroken stream
of consciousness
neither established nor manifesting in this or any other world... This is the fourth attainment of Vision...