The Concept of Congealing

In the Puranas, the moon (pulmonary vein) is said to be "congealed water" and the sun (lobar bronchus) is referred to as "congealed heat," alluding to its expiratory role. 

 In simple terms, this indicates a movement from the distal ends of the lungs towards its hilum. This "involutionary" or "reverse evolutionary" movement  is termed as "congealing." In respect of the waters (the oxygenated flow), it occurs when the smaller pulmonary venous conduits lump together, as it were, into bigger and bigger conduits; the tiny venules congeal into the bigger veins and this occurs for several generations of conduits until finally all the veins merge together, as if, into the primary pulmonary veins. This (congealing)  is therefore a reverse anatomical movement. A similar congealing can occur in respect of the other conduits.