There are many Chinese words whose pronunciation can be represented as "chih" (or, in the modern romanization, zhi) in Chinese:
Heaven (seen here as the ultimate source of all being) falls (duo 墮, i.e., descends into proto-immanence) as the formless. Fleeting, fluttering, penetrating, amorphous it is, and so it is called the Supreme Luminary. The dao begins in the Void Brightening. The Void Brightening produces the universe (yu-zhou ). The universe produces qi. Qi has bounds. The clear, yang [qi] was ethereal and so formed heaven. The heavy, turbid [qi] was congealed and impeded and so formed earth. The conjunction of the clear, yang [qi] was fluid and easy. The congelation of the heavy, turbid [qi] was strained and difficult. So heaven was formed first and earth was made fast later. The pervading essence (xi-jing) of heaven and earth becomes yin and yang. The concentrated (zhuan) essences of yin and yang become the four seasons. The dispersed (san) essences of the four seasons become the myriad creatures. The hot qi of yang in accumulating produces fire. The essence (jing) of the fire-qi becomes the sun. The cold qi of yin in accumulating produces water. The essence of the water-qi becomes the moon. The essences produced by coitus (Yin) of the sun and moon become the stars and celestial markpoints (chen, planets).
The idea that there is a heavier fraction of qi seems to have originated with this passage. Similar ideas show up in the writing of Song dynasty philosopher, particularly Zhu Xi, and there this kind of "materialized lifebreath" is called zhí. Zhu Xi uses the idea of "materialized lifebreath" to explain what we today would call the phenotypical nature of a human being as opposed to the genotypical nature of that human being.