What is Wujishi?
It was the first book in English to discuss, in depth, standing breathing exercise. It is comprehensive to the point of even including case histories of those people who used Wujishi to cure certain illnesses and conditions. It is detailed in the finer points of standing and breathing, micro- and macro-cosmic orbits, Qi movement and something the author refers to as "sticking to the Dan Tian."
And because Cai Song Fang was a longtime student of Master Wang Xuan Jie of Yiquan fame, many Yiquan practitioners consider this book to be a crucial volume in their libraries, especially since books on Yiquan are few and far between.