Life Day

On Page One Fifty eight, Sayadaw discusses how to see the Life-faculty and Sex-element.  Here, he suggests using the eye alone to find the life faculty within its other features (fire, wind, etc.).  While looking up a definition for the life force (Jivitindrya), I came upon this fascinating site: 

We know that we are alive so something is experienced by our consciousness that we can call the Life Force. It is not a magic elixir or spiritual essence. It is a drive to survive. Yes, that is precisely what it is and nothing more. But that force for survival is more elegant than you might suppose. All living creatures possess it, from the simplest plant form to the most complex organism.

In Abhidhamma texts, it is called JIVITINDRIYA, which stems from the pali words “jivita” which is life and “indriya” which is a controlling faculty or principle. It is this Jivitindriya that infuses life into all volition (cetana).
It is twofold, for it includes material life (Rupa-Jivitindriya) and the mental or psychological concomitants (Nama-Jivitindriya). Clearly they are not independent but work together for, as the Abhidamma declares, “Just as a boatman depends upon the boat, even so Jivitindriya depends upon the mind and matter, and that mind and matter depend upon Jivitindriya. 

Sayadaw goes on to suggest wiggling one's finger and noting the consciousness that wants to wiggle the finger. I got a little lost on this page, it seems very short for noticing the life force, not sure about the instructions, but then, I'm in mostly a theoretical mode.