What is meant by "Grasping solid" (握固)?

Grasping solid is a common gesture in Taoist health cultivation.

The method is to hold the thumb with the remaining four fingers into a fist, imitating the shape of a fetus, male left and female right. "Dao Shu zhong Miao pian" said: "what is the one who holds it firmly? I pinch the text of his three fingers with my left and right thumb, or I always hold his thumb with my four fingers and lean between my waist and abdomen with my left and right hands. " Taoism believes that this gesture has the function of promoting the unification of heart and qi and avoiding evil and poisonous qi.